1. She … (to send) that letter a long time ago.
а) have sent
б) had sent
в) was sending
г) sent
2. While she … (to watch) her favourite programme on TV, he phoned his mother.
а) watched
б) was watching
в) had watched
г) had been watching
3. He ... (to wait) for Linda for two hours.
а) was waiting
б) had been waiting
в) had waited
г) waited
4. We ... (to translate) the article by five o'clock.
а) translated
б) had translated
в) was translating
г) had been translating
5. What did you buy at the shop yesterday? — I ... (to buy) a book.
а) bought
б) had bought
в) was buying
г) had been buying
6. I … (to do) some snowboarding, while I … (to ski) in Switzerland, but I … (not to try) ice-skating yet.

1. She sent that letter a long time ago.
   Ответ: г) sent

Объяснение: действие произошло в прошлом и уже завершилось, поэтому используется Past Simple.

2. While she was watching her favourite programme on TV, he phoned his mother.
   Ответ: б) was watching

Объяснение: одно действие длилось в определенный момент в прошлом, а другое произошло во время него. Для длительного действия используется Past Continuous.

3. He had been waiting for Linda for two hours.
   Ответ: б) had been waiting

Объяснение: он ждал Линду в течение двух часов до какого-то момента в прошлом. Это действие продолжалось некоторое время, поэтому используется Past Perfect Continuous.

4. We had translated the article by five o'clock.
   Ответ: б) had translated

Объяснение: перевод статьи был завершен к определенному времени в прошлом (к пяти часам). Используется Past Perfect.

5. What did you buy at the shop yesterday? — I bought a book.
   Ответ: а) bought

Объяснение: действие произошло вчера и полностью завершилось, поэтому используется Past Simple.

6. I did some snowboarding, while I was skiing in Switzerland, but I have not tried ice-skating yet.

Полное предложение:
I did some snowboarding, while I was skiing in Switzerland, but I have not tried ice-skating yet.

Объяснение:

• did some snowboarding — действие в прошлом, которое произошло во время поездки; используется Past Simple.

• was skiing — процесс, который длился в определенный период в прошлом; используется Past Continuous.

• have not tried — действие до настоящего момента еще не произошло; используется Present Perfect.

Ответы:
1 — г) sent
2 — б) was watching
3 — б) had been waiting
4 — б) had translated
5 — а) bought
6 — did / was skiing / have not tried