The correct answer is option 'A': 10 years.

The maturity period of a U.S. Treasury Bond refers to the length of time it takes for the bond to reach its full term and for the principal amount to be repaid to the bondholder. U.S. Treasury Bonds are issued by the U.S. government to finance its operations and are considered one of the safest investment options available. The maturity period of a U.S. Treasury Bond varies depending on the type of bond, but the minimum time it takes for a U.S. Treasury Bond to mature is 10 years.

Here are the key points to consider when understanding the maturity period of U.S. Treasury Bonds:

1. Types of U.S. Treasury Bonds: The U.S. Treasury offers different types of bonds, including Treasury Bills (T-bills), Treasury Notes, and Treasury Bonds. Treasury Bills have a maturity period of less than one year, Treasury Notes have a maturity period of 2, 3, 5, 7, or 10 years, and Treasury Bonds have a maturity period of 20 or 30 years.

2. Maturity Period of Treasury Bonds: Among the different types of U.S. Treasury Bonds, the minimum time it takes for a bond to mature is 10 years. This means that the bondholder will receive the principal amount invested in the bond after 10 years.

3. Longer Maturity Periods: While the minimum maturity period is 10 years, U.S. Treasury Bonds can also have longer maturity periods. For example, some Treasury Bonds have a maturity period of 20 years or 30 years. The longer the maturity period, the higher the interest rate offered on the bond.

4. Interest Payments: U.S. Treasury Bonds pay interest to bondholders semi-annually until the bond reaches maturity. The interest rate is determined at the time of issuance and remains fixed throughout the life of the bond.

In conclusion, the minimum time it takes for a U.S. Treasury Bond to mature is 10 years. However, it's important to note that the U.S. Treasury offers bonds with longer maturity periods, such as 20 or 30 years, providing investors with various options to suit their investment goals and preferences.