the deduction is applicable only for the interests earned from :
(a) a banking company to which the Banking Regulation Act, 1949 (10 of 1949), applies (including any bank or banking institution referred to in section 51 of that Act); (b) a co-operative society engaged in carrying on the business of banking (including a co-operative land mortgage bank or a co-operative land development bank); or (c) a Post Office as defined in clause (k) of section 2 of the Indian Post Office Act, 1898 (6 of 1898),