Correct answer:
d) a certificate of deposit
A mutual fund (not a mutual "friend") is a fund that combines various stocks holdings in the stock market into a single account, thus spreading out the types of stock shares held.
A company stock is also a stock market investment.
A government bond is essentially loaning money to the government for which they pay you interest.
A certificate of deposit is issued by a bank to a bank customer. The money deposited is placed into an account for a specified length of time at a guaranteed rate of interest.