Dear Mark, I’m writing to you from my hotel in Switzerland. I’m having a good time here but you can’t imagine what (1) ______________(happen) to me yesterday. I (2)___________ (be) on the mountain with my friends and we (3) ________________(have) a lovely time because the snow (4) , ___________ (be) perfect for skiing. Unfortunately the sun (5)________ , (shine) on the snow, so it (6) ___________(be) difficult to see. Suddenly, I (7) ___________(hit) a rock and I (8) ______________ (fall) over. Luckily I (9) __________ (not/be) seriously hurt. Now I’m trying to be more carefull I’ll see you when I get back. Best wishes, Jack

В этом письме описывается ситуация “вчера” (то есть прошлое), и по смыслу видно чередование Past Continuous (длительное действие/фон) и Past Simple (короткое действие/событие, которое произошло внезапно или завершилось).

Вот правильные формы:

1. happened

“you can’t imagine what happened to me yesterday” — конкретное событие в прошлом.

2. was

“I was on the mountain…” — состояние/нахождение в конкретный момент в прошлом.

3. were having

“we were having a lovely time” — длительное действие (они проводили время), фон.

4. was

“the snow was perfect” — описание состояния снега (какой он был тогда).

5. was shining

“the sun was shining…” — длительный процесс, фон (солнце светило).

6. was

“so it was difficult to see” — результат/состояние в тот момент.

7. hit

“Suddenly, I hit a rock” — резкое, короткое действие (ударился).

8. fell

“and I fell over” — тоже короткое завершённое событие.

9. wasn’t (was not)

“Luckily I wasn’t seriously hurt” — состояние после падения (не был серьёзно ранен).

Итоговый текст с заполненными пропусками:

Dear Mark,
I’m writing to you from my hotel in Switzerland. I’m having a good time here but you can’t imagine what (1) happened to me yesterday. I (2) was on the mountain with my friends and we (3) were having a lovely time because the snow (4) was perfect for skiing. Unfortunately the sun (5) was shining on the snow, so it (6) was difficult to see. Suddenly, I (7) hit a rock and I (8) fell over. Luckily I (9) wasn’t seriously hurt.
Now I’m trying to be more careful. I’ll see you when I get back.
Best wishes, Jack