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‎1. What made him remarkable as a photographer was his skill in capturing the moment.

2. What made him remarkable as a photographer was his skill of capturing the moment.

3. What made him remarkable as a photographer was his skill at capturing the moment.

Could you tell me which ones are correct?

To me, they're all correct, but according to OED, only q and 3 seem to be correct, but I think 2 is also acceptable.

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No, (2) doesn't sound right. The others are OK.