1. His questions can't be answered
Câu bị động với V khuyết thiếu: can/can't + Vp2
2. He was sent abroad to study chemistry
Câu bị động thì QKĐ: was/were + Vp2
3. Jim asked Tom if his parents were busy
4. I haven't visited Thaland for two years
The last time + S + V(thì QKĐ) + O + was + tg
= S + V(thì HTHT) + O + for/ + tg