The opinion of the court was delivered by
ABBOTT, J.:We granted a petition for review in this case to determine whether the mortgagee is subject to a mortgage registration fee pursuant to K.S.A. 1993 Supp. 79-3102(d)(3). In this case, the mortgagor’s principal indebtedness was included in a previously recorded mortgage on which the mortgagee had already paid a mortgage registration fee. The original lender/mortgagee then *192assigned this mortgage. The mortgagor has now returned to the original lender to refinance the loan. The question at issue is whether the mortgagee is subject to a second mortgage registration fee when the new mortgage, which has been refinanced with the original lender and which includes the principal indebtedness from the original loan, is filed. The statute at issue, which answers the above questions, is K.S.A. 1993 Supp. 79-3102(d)(3). It provides:
“(d) No registration fee whatsoever shall be paid, collected or required for or on: (3) any mortgage or other instrument upon that portion of the consideration stated in the mortgage tendered for filing which is verified by affidavit to be principal indebtedness covered or included in a previously recorded mortgage or other instrument with the same lender or their assigns upon which the registration fee herein provided for has been paid.”
The Board of Tax Appeals, the District Court of Riley County, Kansas, and the Kansas Court of Appeals have all held the mortgagee is exempt from the registration fee by reason of K.S.A. 1993 Supp. 79-3102(d)(3). A majority of this court agrees.
The facts are not in dispute and are fully set forth in the Court of Appeals’ opinion, In re Application of Zivanovic, 22 Kan. App. 2d 184, 913 P.2d 224 (1996). Highly summarized, the Zivanovics borrowed money from the First State Bank and gave a mortgage. The First State Bank paid the mortgage registration tax and assigned the note to a second financial institution, which assigned the mortgage to a third financial institution. Both assignments were recorded.
The Zivanovics then refinanced the note and mortgage with the original lender, the First State Bank, and Riley County collected a mortgage registration fee. The procedural history, as set forth in the Court of Appeals’ opinion, followed.
A majority of this court agrees with the Court of Appeals’ opinion and adopts the same. We have additional thoughts on the subject.
A majority of this court is of the opinion that two principles of law are applicable. The first principle is that it is the function of a court to interpret a statute to give it the effect intended by the legislature. Amoco Production Co. v. Armold, Director of Taxation, 213 Kan. 636, Syl. ¶ 4, 518 P.2d 453 (1994). The second principle is that
*193“BOTA is a specialized agency that exists to decide issues concerning taxation and valuation; its decisions should be given great credence and deference when it is acting in its area of expertise. In re Tax Appeal of Director of Property Valuation, 14 Kan. App. 2d 348, 353, 791 P.2d 1338 (1989), rev. denied 246 Kan. 767 (1990). The ruling of an administrative agency on questions of law, while not as conclusive as its findings of facts, is nonetheless persuasive and may carry with it a strong presumption of correctness. Boatright v. Kansas Racing Comm’n, 251 Kan. 240, 246, 834 P.2d 368 (1992). However, if the reviewing court finds that the administrative body’s interpretation of a question of law is erroneous as a matter of law, the court should take corrective steps. 251 Kan. at 246. The party challenging the validity of the agency’s action bears the burden of proving the invalidity of the action. K.S.A. 77-621(a)(1).” Hixon v. Lario Enterprises, Inc., 257 Kan. 377, 378-79, 892 P.2d 507 (1995).
“Usually, interpretation of a statute by an administrative agency charged with the responsibility of enforcing that statute is entitled to great judicial deference. State Dept. of SRS v. Public Employee Relations Board, 249 Kan. 163, 166, 815 P.2d 66 (1991). The agency’s interpretation of a challenged statute may, in fact, be entitled to controlling significance in judicial proceedings. Further, if there is a rational basis for the agency’s interpretation, it should be upheld on judicial review.” Kansas Univ. Police Officers Ass’n v. Public Relations Bd., 16 Kan. App. 2d 438, 440, 828 P.2d 369 (1991).
See also State Dept. of Administration v. Public Employees Relations Bd., 257 Kan. 275, 281, 894 P.2d 777 (1995); In re Tax Appeal of Harbour Brothers Constr. Co., 256 Kan. 216, 221-22, 883 P.2d 1194 (1994).
K.S.A. 79-3102 (Ensley 1984) was amended in 1985. Prior to its amendment in 1985, 79-3102 read that no registration fee shall be paid, collected, or required on any mortgage or other instrument “upon that portion of the consideration stated in the mortgage tendered for filing which is verified by affidavit to be principal indebtedness covered or included in a previously recorded mortgage or other instrument with the same lender upon which the registration fee herein provided for has been paid.”
It would appear clear to us that prior to the amendment to 79-3102 in 1985, the mortgage presently before us would have been exempt from a registration fee because the principal indebtedness was included in a previously recorded mortgage with the same lender upon which the statutory registration fee had already been paid. The fact that the same lender had assigned the mortgage would appear irrelevant. What would be relevant is that the mort*194gagee had already paid the registration fee on the money secured by the loan.
The 1985 legislature amended 79-3102 (H.B. 2354) to exempt mortgages given to development corporations certified by the United States Small Business Administration (SBA). All of the legislative history of H.B. 2354 deals with the SBA exemption.
In 1985, 79-3102 was amended. The words “or their assigns” were inserted after the words “the same lender.” There is no legislative history to explain why or by whom these words were inserted. It is clear that the Kansas Bankers Association supported H.B. 2354 and in fact submitted an amendment to it that was adopted. If the legislature had intended to change the statute to charge banks a second registration fee on the same funds, one would expect the legislative history to reflect at least a mild protest from the banking industry. There is no indication from any legislative history that the legislature intended to make any change in 79-3102 other than to give “assigns” the same exemption extended to the original lender who paid the registration fee.
The legislature does not ordinarily knowingly require a useless act. Here, both parties agree that had the mortgage been reassigned to the First State Bank prior to executing the replacement mortgage, a second registration fee would not have been assessed. While reassigning the mortgage to the original lender before executing the replacement mortgage would cost time, money, and effort, there is no legal reason to do so and nothing would be gained by this act. Why would the legislature require a useless act to save the mortgagee from having to pay a second registration fee? The majority of this court does not think the legislature would or did impose such a useless requirement on a mortgagee. If the legislature did not want to grant a registration fee exemption in this situation, it could have simply repealed the exemption or stated that the “same lender” does not receive the exemption unless the lender is the present holder of the original mortgage.
Based on legislative intent and deference to the Board of Tax Appeals, we hold the mortgage registration fee exemption of K.S.A. 1993 Supp. 79-3102(d)(3) applies to an original lender, even if the *195lender has assigned the original mortgage and no longer holds it at the time the second mortgage is filed.
Affirmed.