The powers that are exercised by both the national government and state governments at the same time are called concurrent powers. These powers are shared between the two levels of government and can be exercised simultaneously. To determine which of the options is the correct answer, we need to know the definitions of all four terms:
A. Concurrent powers: As explained above, these are powers that are exercised by both the national government and state governments simultaneously.
B. Enumerated powers: These are powers explicitly listed in the United States Constitution that are granted to the national government. Examples include the power to coin money, declare war, and regulate interstate commerce. These powers are not shared with the state governments, so option B is not the correct answer.
C. Prohibited powers: These are powers that are specifically denied or prohibited to both the national government and state governments. For example, the Constitution prohibits the government from passing ex post facto laws or granting titles of nobility. However, these powers are not exercised by both levels of government at the same time, so option C is not the correct answer.
D. Reserved powers: These are powers that are not granted to the national government and are therefore reserved for the states, as stated in the Tenth Amendment of the United States Constitution. Examples of reserved powers include the power to conduct elections, establish local governments, and regulate intrastate commerce. While these powers are exercised by the state governments, they are not shared with the national government, so option D is not the correct answer.
Based on the explanations above, the correct answer to the question is A. concurrent powers.