... ) tested Compare the sentences in pairs and try to figure out how passive voice works Then, change these sentences to passive voice: They chop down trees _ They use up all ... have tested only some of the chemicals used in industries B Do the same to these corresponding PASSIVE VOICE sentences a b c d e f This system ( ) is ( ) called materials economy In extraction, natural ... perceived obsolescence? c What’s their importance in the system? PART IV – GRAMMAR A In the ACTIVE VOICE sentences below, write the corresponding number for each verb tense Present simple Past simple...