Как ответить на почему урок для меня сложный

1. He has forgotten his Spanish .1. since .. he left Cuba.
2. What have you done ..1. since . I last saw you?
3. I haven't seen him . 2. for.. ages.
4. It has rained ..1. since . Monday.
5. I have known him ..1. since . childhood.
6. I've known him 2. for... years.
7. - How long have you been here?
- I've been here . 2. for.. two months, ..1. since . last May.
8. - How long have you studied Chinese?
- Oh, . 2. for.. five years, ..1. since . I was eighteen.
9. - How long have you been in the library?
- I've been here ..1. since . ten o'clock, . 2. for.. three hours.
10. Peter is hungry because he has had nothing to eat . 2. for.. five hours, ..1. since . morning.
11. They have been here . 2. for.. an hour.
12. It's been foggy . 2. for.. a fortnight.
13. ..1. since . when has he been in love?

Hi Mike,
Would you like to spend a good time at my granny's dacha? We can stay there the whole weekend. You don't have to take any food, as granny has plenty of it in her greengarden. Still, there is a good shop nearby in case we need something extra. As you may remember, there is a small lake about half a mile from her dacha. So, don't forget to take your swimming trunks and sun-cream. If it's OK with you, let me know and we will pick you up when we are going there on Friday evening.
I'm wating for your phone call,
 6010592