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How do you reduce the adjective clause? I don't know how to change the verb in this sentence after we omit the relative pronoun.
It is not my homework. I read somewhere that we omit the relative pronoun and the form of verb be and any other accompanying auxilliary and if we don't have the form of verb be we change the verb into -ing form and here we have present perfect and I don't know whether I should change it into -ing form or -having +pp?