Once Congress has passed a law. the president may block or prevent it from taking effect. This is called. A. committee
B. Action
C. Hearing
D. Veto

The answer is D. Veto.

Explanation:

The definition of veto itself is "The procedure established under the Constitution by which the president refuses to approve a bill or joint resolution and thus prevents its enactment into law. A regular veto occurs when the president returns the legislation to the house in which it originated." - www.senate.gov

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