Answer: b. interest rates
Explanation:
Interest rates are known as the sum of money which a borrower pays to a lender for borrowing money from him.
The Central Bank helps the economy to grow by lending money to commercial banks at a low interest rate. Furthermore, people also borrow more money from commercial banks because they also give out loan to them at a low interest rate. Thus, this leads to increase in the amount of money in the economy which makes it to grow.