9. Раскройте скобки, употребляя глаголы в Past Continuous. 1. While I (to copy) the exercise, my friends (to describe) a picture. 2. When we came in, the children (to clean) their desks. 3. We met her at the bus stop. She (to wait) for the bus.4. Some of the children (to ski) while other children (to skate). Everybody (to have) a lot of fun. 5. When we came the family (to get) everything ready for Christmas. Bob and Helen (to decorate) the Christmas tree. 6. The girls (to feed) the birds in the garden while the boys (to make) a bird-house.

1. While I was copying the exercise, my friends were describing a picture.

2. When we came in, the children were cleaning their desks.

3. We met her at the bus stop. She was waiting for the bus.

4. Some of the children were skiing while other children were skating. Everybody was having a lot of fun.

5. When we came, the family was getting everything ready for Christmas. Bob and Helen were decorating the Christmas tree.

6. The girls were feeding the birds in the garden while the boys were making a bird-house.

Немного пояснений, почему именно так:
Past Continuous образуется с помощью was/were + глагол с окончанием -ing и используется, когда действие:

• шло в определённый момент в прошлом (When we came in, the children were cleaning their desks — они были в процессе уборки);

• два действия одновременно происходили в прошлом (While I was copying, my friends were describing);

• подчёркивается длительность, процесс (She was waiting for the bus — она стояла и ждала какое-то время).