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She was reminiscing __ the party. (over, about or around).
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Which do you choose? (You can also google 'reminiscing' and see what prepositions follow the word.)
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By the process of elimination, "about" is the best word. That is the preposition used most often after "reminisce."

which preposition comes after the word reminiscence?

We take pride in the reminiscence _____ our pioneers of science

Reminisce

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