Answer:
a. grand jury
Step-by-step explanation:
For an impeachment process to be completed in the US, the process must pass a vote in the House of Representatives and, if approved, a Senate judgment. President loses office only if two thirds of senators vote in favor of cassation.
During an impeachment process, the House of Representatives must vote whether to approve the President's request for removal or not. In this case, the work of the Representatives resembles the work of a Grand Jury who must vote whether or not to approve a defendant.
Representatives debate and vote on the articles of the impeachment process in one session. In the House, a simple majority is enough - that is, 218 of the 435 deputies must vote in favor of condemning the president.