Respuesta :
Correct Answer: a. Macbeth has become terribly suspicious and trusts no one; he sends the third murderer to make certain the job gets done.
Explanation: The two hired murderers are joined by a third at the beginning of scene 3 because Macbeth is paranoid. We know this because he told his wife that his mind is "full of scorpions", which means that Macbeth cannot rest while Fleance and Banquo are alive.