6. 4) Paul can ride a bike.
5) Pilots can fly planes.
6) I couldn't sleep well last night.
7. text 1. 2) Could visit
3) Could do
4) Couldn't collect
5) Couldn't see
6) Couldn't do lots of things.
text 2. 2) can't go
3) can't buy
4) can walk
5) can hear
8. When I was four I could play football all day. I couldn't read books, I couldn't whistle, I couldn't speak English, of course, I couldn't swim in the swimming pool.
Now I can read books, I can go to school, I can swim, speak English well, cook. But unfortunately, I can't play football all day because of lack of free time.