=>
3/
1. studied ( just as : ngay khi, đúng lúc -> diễn tả 2 hành động xảy ra gần như cùng một thời điểm)
2. has worked ( since -> HTHT)
3. meeting (look forward to Ving)
4. to be taken ( want sth to be V3/ed)
5. would visit ( câu ước)
6. destruction : sự phá hủy
7. polluted ( be adv adj)
8. clean
4/
1. can -> could
2. is -> was
3. fewer -> less
4. after -> before
