Final answer:
An interest rate is what it costs to borrow money from a lender, not related to the reserve requirement or the Federal Reserve's charges to banks directly.
Step-by-step explanation:
An interest rate is c) what it costs to borrow money from a lender. It is not the percentage of reserves a bank is required to hold, nor the amount of money in circulation, nor the percentage that the Federal Reserve charges its member banks. However, the Federal Reserve does influence interest rates by setting the discount rate, which is the interest rate the Federal Reserve Bank charges commercial banks for loans. The reserve requirement refers to the percentage of deposits banks are legally required to hold as reserves and affects how much money they have available to lend out.