Which of the following is a true statement?

a. The federal government in the U.S. retains all powers not specifically delegated to the states.

b. The federal government in the U.S. cannot regulate commerce within a state, even if the commerce concerns more than one state, since states existed before the federal government.

c. When state regulations in the U.S. impinge on interstate commerce, commerce must yield to the state regulations, no matter how heavy the burden placed on interstate commerce, since states have the right to control activities within their border.

d. Some constitutional protections in the U.S. apply to business entities such as corporations.