The correct answer is answer A ("The Mousetrap").
Hamlet shows King Claudius a play called "The Moustrap". The plot it presents, recreates very closely the conditions of the actual murder of Hamlet's father. By having it performed for Claudius, he's trying to discover whether Claudius is guilty of the murder or not.
The name of the play puts Claudius as the mouse falling into Hamlet's trap.
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