He is good at English/his English is very good

English as a Second Language English Vocabulary, Grammar and Idioms
1
  1. He is good in/at English.
  2. He is weak in/at English.
  3. He is poor in/at English.
  4. He is strong in/at English.

Which is the correct preposition in each case?

Thanks.

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2

The first should have at because we say good at. So also bad at.
The words weak and poor can take in in 2 and 3.
The fourth is not found to be a formal collocation. We say proficient in or fluent in English. (However, strong on is seen to be acceptable)

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