7.6 past simple, past perfect 1. Once they mapped / had mapped the genome, they began / had begun working on the treatment. 2. When the final tests were / had been started, the children were already / had already been under observation for six months. 3. In that period national liberation movements existed / had existed , but the social structures were not yet / had not yet been completely put into place. 4. Subjects listened to and imagined words. They then attempted / had attempted to discriminate words they hear / had heard from words they imagined / had imagined . 5. They realized / had realized that they did not collect / had not collected enough specimens to enable them to do the study. 6. The students were / had been near the end of an eight-week research project in which they analyzed / had analyzed the data that they collected / had collected on the frequencies of traffic accidents on town roads. 7. We noted that they did not assess / had not assessed the cardiac functions of the patients but only controlled / had onlycontrolled for bias. 1. had mapped, began 2. were, had already been 3. existed, had not yet been 4. attempted, had heard, had imagined 5. had not collected 6. were, had analyzed, had collected 7. had not assessed, had only controlled
