What is the main rationale that Brutus gives in his act 2.1 soliloquy in The Tragedy of Julius Caesar to explain his involvement in the assassination plot against Caesar?

Brutus admits that he has no proof Caesar is already acting like a tyrant. Instead, he fears what Caesar may become if he is crowned: power could change him, as a ladder-climber may turn away from those who helped him once he reaches the top. This reasoning is captured by choice B, which says Caesar may become a tyrant because power will let him behave tyrannically.

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