Why would a mutual fund, a collection of stocks, bonds and other securities have less risk than investing in stock alone

Because of the nature of risk associated with investing in the Stocks.

Explanation:

Investing in more than one funds, like mutual funds, a collection of stocks and bonds, etc, is a technique to divide the risk over different investments. Investing only in one investment whose nature is pretty volatile like stocks, is very risky. If a person invests in one volatile investment like Stocks, he is more likely to bear high risks. So investing in more than one thing will divide the risk associated with investing in one stock alone. So it is always preferable to divide your risk by investing in more than one investments.

answer; i believe the correct answer is (treasury bills);