1. Have you ever done

2. did

3. has collected

4. helped

5. have known

1. Have you ever done volunteer work?

Dấu hiệu nhận biết: ever => thì hiện tại hoàn thành

2. Yes, I did volunteer work last month

DHNB: last month => thì quá khứ đơn

3. Mr.robinson has collected hundreds of books and clothes for street children so far

DHNB: so far => thì hiện tại hoàn thành

4. Going home from school yesterday .i helped an old man go across thr street

DHNB: yesterday => thì quá khứ đơn

5. Linh is my close friend.we have known each other for 5 years.

DHNB: for => thì hiện tại hoàn thành