Answer: C. Five year certificate of deposit.
Explanation:
A certificate of deposit refers to a savings account whereby a fixed amount of money is being held for a fixed period of time, and interest is earned on it.
Since Joan Martin expects interest rates to decline over the next few months, in order to achieve her long-term financial goals, then she will trade off liquidity for a higher return by using a five year certificate of deposit. Here, the liquidity is low when it's compared to that of the regular savings account.