Congress passed a bill prohibiting the President from granting a pardon to any person who had not served at least one-third of the sentence imposed by the court which convicted that person. The President vetoed the bill, claiming that it was unconstitutional. Nevertheless, Congress passed it over his veto by a two-thirds vote of each house. This act of Congress is 
constitutional, because it was enacted over the President's veto by a two-thirds vote of each house.  constitutional, because it is a necessary and proper means of carrying out the powers of Congress.  unconstitutional, because it interferes with the plenary power of the President to grant pardons.  unconstitutional, because a Presidential veto based upon constitutional grounds may be overridden only with the concurrence of three-fourths of the state legislatures. 
Question: Congress passed a bill prohibiting the President from granting a pardon to any person who had not served at least one-third of the sentence imposed by the court which convicted that person. The President vetoed the bill, claiming that it was unconstitutional. Nevertheless, Congress passed it over his veto by a two-thirds vote of each house. This act of Congress is 
A. constitutional, because it was enacted over the President's veto by a two-thirds vote of each house. 
B. constitutional, because it is a necessary and proper means of carrying out the powers of Congress. 
C. unconstitutional, because it interferes with the plenary power of the President to grant pardons. 
D. unconstitutional, because a Presidential veto based upon constitutional grounds may be overridden only with the concurrence of three-fourths of the state legislatures. 
Answer: