Answer:
Both Houses
Explanation:
A presidential veto can be overridden by a two-thirds vote in both houses of Congress. This is taken from the U. S. Senate website itself:
"The process by which each chamber of Congress votes on a bill vetoed by the President. To pass a bill over the president's objections requires a two-thirds vote in each Chamber. Historically, Congress has overridden fewer than ten percent of all presidential vetoes"
