1. Mary (be) has been seriously ill since last night. (thì hiện tại hoàn thành: S + have/has + Ved/c3 + ...)
2. They sometimes (go) go school by bus. (thì hiện tại đơn, chủ ngữ số nhiều thì động từ vẫn giữ nguyên)
3. How long have you (study) studied English? (HTHT nghi vấn wh_q:
- I (study) have studied it for 7 years.
4. We last (see) saw them last Sunday. (thì QKĐ)
5. I (not meet) haven't met him since he moved to Hanoi. (HTHT phủ địng: S+haven't/hasn't+Ved/c3+ ....)