Who regulates markets where investments are traded?

The one who regulates the market is the Federal Government.

Explanation:

The US has federal system, in which some of the powers are given to the federal government, and others are given to the states. Congress, and the other two branches of the federal government, can only exercise those powers given in the Constitution. The powers of Congress are enumerated in the Constitution, and Article I, Section 8 specifies the power of the Congress to "regulate commerce among the several states" as well as regulate commerce with foreign nations and to regulate commerce "with Indian Tribes."

the correct answer is a