The political candidate admitted to smoke marijuana in his youth.
The political candidate admitted (to) smoking marijuana in his youth. This is fine. The "to" is optional.
The political candidate admitted that he liked to smoke marijuana in his youth. This is grammatically okay, but you have inserted information that was not in the first sentence.
The political candidate admitted that he smoked marijuana in his youth.
Top answer
As usual, it is difficult to find fault with GG's advice.
— Philip
As usual, it is difficult to find fault with GG's advice.
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