Why does Hamlet refer to Rosencrantz as a sponge

In Hamlet, Rosencrantz is referred to as a "sponge" because he has soaked up all the benefits of Claudius's authority. In saying this, Hamlet wants his friend to know that he doesn't trust him and that he regards him as just another one of Claudius's lackeys.

Explanation:

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1, 4, and 5 are all conflicts

the correct answer is (a) . answer should be simple, clear and brief.