1. have been visited

2. has

3. symbolizes

4. is celebrated

5. have visited

Ex 3.

1. Radioactive pollution is very dangerous since it can cause abnormal growth.

2. Leaves are damaged because the tree cannot get enough ___ energy to stay healthy.

Ex2:

1.Four countries.....have been visited....(visit) by John so far.

2. London ......has...(have) a population of eight million people.

3. The Statue of Liberty in New York is a monument which .........symbolizes..........(symbolize) freedom.

4. Vietnam’s Independence Day ........is celebrated.......... (celebrate) on September 09th.

5. We ............have visited........... (visit) Sydney Opera House for several times.

Ex3:

1. Radioactive pollution is very dangerous since it can cause abnormal growth
2. because Leaves are damaged  the tree cannot get enough food energy to stay healthy

2. Leaves are damaged because the tree cannot get enough food energy to stay healthy.

 câu 2 :đặt hai chỗ chỗ nào cũng đc nhá