В упражнениях среднего уровня надо уже думать грамматике, в данном случае, какое именно прошедшее время уместно употребить в том или ином случае. Но подсказок в предложении хватает, поэтому трудностей не предвидится. В следующих предложениях надо раскрыть скобки и поставить глаголы в Past Indefinite Tense или Past Perfect Continuous Tense. В конце упражнения и раскрою скобки и напишу предложения в нужном времени, чтобы вы могли себя проверить.
1. Jack ( to drop) the pencil he ( to write) with.
2. They (to drive) in the car for a long time before they (to come) to the crossroads.
3. He ( to know) from the redness of her eyes, there ( to be) times she ( to cry).
4. The scientists ( to carry ) out dozens of experiments before they ( to achive) satisfactory results.
5. Turning away, Ann (to move) to close the cupboard her husband ( to look) into.
6. The violinist ( to practise) the passage hour after hour until he ( to master) it at last.
7. The weather was cold as the severe wind ( to blow) since yesterday.
8. At last John ( to bring) me the books which I ( to expect) several days.
9. The children were tired as they (to play) football for several hours.
10. He ( to write) and ( to tear) up more than one letter when at last he ( to find) the necessary form of address.