1. Nowadays, the recycling of high tech garbage is becoming / was becoming a big concern.
2. Klaus Brodersen is trying / was trying to produce a definite classification of what chemicals should and should not be allowed in the production of high tech equipment.
3. The manufacturer Loewe was developing / has developed a green TV which contains just 39 grams of plastic.
4. We were discussing / discussed the problems of pollution at 2 o’clock yesterday.
5. When I came in, he was explaining / explained the details.
6. While we were helping / helped, they were talking.
7. People worked / were working hard many years ago.
15.Some of the following sentences contain mistakes. Find the mistakes and correct them.
1. While they were carrying out tests in the laboratories, researchers were analysing past results.
2. The Romans built roads of layers of broken stones of various sizes and were covering them with flat stones.
3. Louis Pasteur was discovering the action of germs while he was studying fermentation in wines.
4. While we were studying the airbags, we made a significant discovery.
5. While our team was studying performance of the car, another team looked at the characteristics.
6. She was steering the boat while he was sleeping.
7. I repaired my motorbike at 3 o’clock yesterday.