... describe. relative pronoun is necessary relative pronoun is not necessary Relative clauses - defining or non-defining? Study the situations and then decide whether the following relative clauses ... which we visited yesterday, is very old. Non-Defining Relative ClausesCombine the sentences using relative clauses. Note that all relative clauses are non-defining.1. Samuel Johnson was the ... you want to send it. relative pronoun is necessary relative pronoun is not necessary 5. The Thames is a river which runs through London. relative pronoun is necessary relative pronoun is not...