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.