Mobile homes, pulled by specially designed trucks have been increasing in numbers allover

the United States. Often, driving along, you can see some mobile homes high on a hill. Some stand under trees along a river or a lake. They're wonderfully built homes. Sometimes they're as much as 40 feet long, with two to five rooms, and you can find many things you need in them. When you park your mobile home, water, electricity power and telephones are connected, and you can enjoy yourself there. The fact that these homes can be moved doesn't mean that they do move all the time. Sometimes their owners stay for years in one place, plant gardens, build walls and so on. These homes are often quite expensive. Some even cost $ 20,000. Why does a family choose to live in such a home？ Well, it's comfortable, easy to keep clean, easy to keep warm, no need to paint. What's more, the fast increase of mobile homes in numbers has something to do with the job uncertainty (不稳定性). Nobody knows what will happen tomorrow. If a factory closes down, you may be trapped with the house you can't sell. However, if you have a mobile home, you can move on easily. The greatest selling attraction of these mobile homes is that they can be improved every year. If you're doing well, you may change a new model just as you do with a car. There is a ready market for used ones, so the price of the mobile homes is higher than that of automobiles (汽车).

16. From the passage, we know that mobile homes _______.

A. can be built better than our homes

B. need to move all the time

C. can provide something people need

D. must stand only high on a hill

17. _______ is one of the reasons for people to choose mobile homes.

A. The job uncertainty

B. The strange design

C. The low price

D. The high speed

18. Which of the following may NOT attract people to buy mobile homes？

A. The new model appears every year.