We don't use 'that' in non-defining relative clauses, so we need to use 'which' if the pronoun refers to a thing, and 'who' if it refers to a person. We can't drop the relative pronoun in this kind of clause, even if the relative pronoun is the object of the clause.

theory-of-relative-clauses-and-exercises-will-help-you-improve-your-grammar_149125.pptx

Theory of relative clauses and exercises will help you improve your grammar.

theory-of-relative-clauses-and-exercises-will-help-you-improve-your-grammar

Let's do English ESL general grammar practice. We don't use 'that' in non-defining relative clauses, so we need to use 'which' if the pronoun refers to a thing,…