2. It is polite       a gift when you visit somebody for the first time.

   A. take   B. taking   C. to take   D. to taking

1. With the help of his friends,he changed a lot. Maybe that’s the of       friendship.

   A. station   B. power   C. decision   D. invention

3. Electricity        ( flow) through thin wires.

4. The toy car gets power from        (battery) .

5. Trees can produce        ( chemistry ) to protect themselves from insects.

l. The thick wire is        (connect) to the power station.

2. 1 think you can buy something in        (packet) .

3. You can’t see cables because they are u        the ground.

4. We should speak p        to our teachers.

5. If you r        to a question,you answer it.

1. We call the thick wires under the street c   .

2. He looks f        to make such a mistake.

5. 我们需要太阳能。

We need             .

4. 电池里面的化学物质产生电。

The                    produce electricity.

3. 这些与街道下面的电缆相连。

These                     cables under the street.

2. 在某种程度上，它像水。

It is like water ,                    .