The correct answer is A. U.S treasury bonds.
U.S. Treasury bonds are considered to be the safest investment in the world because they are backed by the full faith and credit of the United States government. This means that the U.S. government is obligated to pay back the principal and interest on these bonds, even if it means raising taxes or cutting spending.
Mortgages are loans that are used to finance the purchase of a home. They are considered to be a riskier investment than U.S. Treasury bonds because there is a risk that the borrower may default on the loan.
Municipal bonds are loans that are issued by state and local governments. They are considered to be a less risky investment than corporate bonds because they are exempt from federal income tax.
Corporate bonds are loans that are issued by companies. They are considered to be the riskiest investment of the four options because there is a risk that the company may default on the loan.