that or which / relative
Answer key says we can not use 'which' in the following sentence.

-This is the time of year ..*that*.. everyone seems vulnerable to catching coughs and colds.-

I really didn't get it.Why is 'that' correct while 'which' is not ?

Question

that or which / relative
Answer key says we can not use 'which' in the following sentence.

-This is the time of year ..*that*.. everyone seems  vulnerable to catching coughs and colds.-

I really didn't get it.Why is 'that' correct while 'which' is not ?

Answer

"Which" is incorrect, the answer is "that" or "when".

https://https://learnenglish.britishcouncil.org/en/english-grammar/relative-clauses

Answers · 2