In Marbury v. Madison, the Supreme Court first stated the principle that (8.18a) A) Only the courts may regulate interstate commerce
B) The president may veto federal legislation
C) The courts may declare a federal law unconstitutional
D) Only the president may issue an executive order

C) The courts may declare a federal law unconstitutional.

Explanation:

The famous Marbury v. Madison case was a result of the conflicting interests of the outgoing and the incoming president. And this case also led to the Supreme Court dictating the possibility of the courts declaring any law unconstitutional if it deems it against the interest of the constitution.

Outgoing president John Adams made "midnight appointments" to several of his supporters including William Marbury. But while Marbury and some others' commissions were not carried out within the period of Adams' presidency, Marbury filed a petition against the new Secretary of State John Marshall to deliver his commission. But Marshall refused, stating that with the new administration under President Jefferson, the orders were not valid. This resulted in the court dictating judicial review of any law that may be deemed unconstitutional.

Therefore, the correct answer is option C.

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