Question

Hamlet is seen as being indecisive throughout the first three acts of the play. Which of these lines from acts IV and V show that Hamlet is finally focusing on revenge?
A) HAMLET: ... Of thinking too precisely on the event— A thought which quarter'd hath but one part wisdom And ever three parts coward—I do not know (Hamlet, act IV, scene IV)

B) Which is not tomb enough and continent To hide the slain?—O, from this time forth, My thoughts be bloody, or be nothing worth! (Hamlet, act IV, scene IV)

C) Our indiscretion sometime serves us well When our deep plots do pall and that should teach us (Hamlet, act V, scene II)

D) Without debatement further, more or less, He should the bearers put to sudden death, (Hamlet, act V, scene II)

Answer 1

I would say the correct answer is B) Which is not tomb enough and continent To hide the slain?—O, from this time forth, My thoughts be bloody, or be nothing worth! (Hamlet, act IV, scene IV) 
He says in this line that he should be bent on revenge and finally go through with it and stop dwelling on whether or not he should do it. And after that scene he does actually start making plans for Claudius' murder, which does happen in the end when almost everyone actually dies.