The correct answer is A) The president.
When a bill passes both the Senate and House of Representatives (aka Congress), it is then sent to the president to be signed. Then, in order to become law, the president must approve of the law. The only loophole around this would be if the president vetoed the law. If the president vetoes a bill (aka stops it from becoming a law) the bill then goes back to Congress. From there, Congress can override this veto by passing it through a 2/3rd's majority vote in both the House of Representatives and the Senate.