We use defining relative clause to identify a thing or a person that is being talked about. To refer to people that and who can be used. To refer to things that and which can be used. If we speak about superlatives or the words like something, someone, anyone, everything, we should use that only. Commas aren’t used in defining clauses.

Упражнения к этому уроку
Ми працюємо, сплачуємо податки та допомагаємо один одному

Грамматика с Максимом Ачкасовым

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IELTS Tips & Practice Tests (General Reading)