I.
21.→Their complaints should be sent to the main office.
22.→Your car might have been stolen if you had left the keys in it.
23.→The fire could have been caused by a short circuit.
24.→This mail could be sent on time.
25.→Should that news be announced as soon as possible?
26.→The scientific book has to be returned to the library by Phong.
27.→The memorial monument will be rebuilt by the government.
28.→Papers written in pencils won't be accepted by the teacher.
29.→She might be interviewed by the principal.
II.
1.in/in
11.on
2.on/at
12.at
3.on
13.before
4.on
14.from/to
5.since
15.at hoặc in
6.for
16.between/and
7.off/and
17.when
8.to/on
18.in
9.at
10.for
chúc em học tốt!!!!!