Question

6 They have been friends for/since many years. 7 What were you doing/had you done at six o'clock yesterday? 8 By the time I went to the cinema, the film was already starting/had already started. 9 Listen! Someone sings/is singing! 10 Bill watched/was watching TV while I was reading a magazine. ​

Answer 1

6. for. (Они дружили на протяжении скольких-то лет).
7. were you doing. (Длительное действие, поэтому past continuous).
8. had already started. (Действие завершилось и предшествует другому действию в прошлом).
9. is singing. (Поет в данный момент, поэтому present continuous).
10. was watching (два длительных действия)

Answer 2

6. "They have been friends for many years" means that they have been friends for a long time and the friendship has continued up until the present. The duration of their friendship is emphasized.

7. "What were you doing at six o'clock yesterday?" is asking about a specific action or activity that was happening at a particular time in the past. The question is referring to a single action or event that occurred at six o'clock yesterday.

8. "By the time I went to the cinema, the film was already starting" suggests that when the speaker arrived at the cinema, the film had just begun or was about to start. The action of the film starting had already happened in relation to the speaker's arrival at the cinema.

9. "Listen! Someone is singing!" indicates that at the moment of speaking, someone is currently singing. The action is happening in real time.

10. "Bill watched TV while I was reading a magazine" means that Bill was engaged in the activity of watching TV while the speaker was simultaneously engaged in the activity of reading a magazine. The two actions were happening at the same time in the past.