Cau V.

1. Yes, it is

2. The most common use of electricity is providing artificial lightning.

3. People use electricity for television sets, computers, electric fans, irons and many other applicances at home.

4. If there were no electricity, modern man would be lost.

Cau VI.

1. I suggest meeting inside the center, at the cafe's corner. 

2. It's important to keep the environment clean.

3. Unless some one puts the coal in, the fire will go out.

4. How about planting some trees around your house to get more fresh air?

Cau III.

1.Unless you study harder, you (not pass) won't pass the final exam.

2.He suggests (take) taking the bus to school.

3.She has never eaten (eat) this kind of this food before.

4.We are looking forward to (hear) hearing from you.