The choices for this question are:
A) rejecting candidates for the Supreme Court
B) overriding a veto
C) using a veto
D) declaring laws unconstitutional
The correct answer is C.
A is wrong because the Supreme Court belongs to the judiciary branch. B is wrong because the president does not have that power, only Congress does. D is wrong because that is the check the judiciary has over Congress.
C is correct because that's how the president checks Congress power: it can use his/her power to veto a bill he/she believes it's bad for the nation. And Congress, on the other hand, can override the veto. That's how part of the checks and balances between Executive and Legislative works.