1. We (sleep) had been sleeping for 12 hours when he woke us up. Ans: had been sleeping

2. They (wait) had been waiting at the station for 90 minutes when the train finally arrived. Ans: had been waiting

3. We (look for) had been looking for her ring for two hours and then we found it in the bathroom. Ans: had been looking for

4. I (not / walk) had been walking for a long time, when it suddenly began to rain. Ans: had been walking

5. How long (learn / she) had been learning English before she went to London? Ans: had been learning

6. Andy Lau caught the flu because he (sing) had been sitting in the rain too long. Ans: had been sitting

7. He (drive) had been driving less than an hour when he ran out of petrol. Ans: had been driving

8. They were very tired in the evening because they (help) had been helping on the farm all day. Ans: had been helping

9. I (not / work) had been working all day; so I wasn't tired and went to the disco at night. Ans: had been working

10. They (cycle) had been cycling all day so their legs were sore in the evening. Ans: had been cycling