用括号内所给词的适当形式填空。

1. — The             (develop) of new products is important to our company. Do you know?

    — Yeah, it is our duty to try our best to deal with it.

2. I think the most helpful             (invent) is the light bulb (电灯泡). It gives people more time to work and

     play.

3. The foreigner spoke English so             (quick) that I could hardly understand what he said.

4. The large population of China has caused many             (difficult). For example, many farmers have no

    farmland to grow crops on.

5. — What do you think of the English             (train) school? 

    — It is great. I have improved my English a lot.