C．bottom­like D．gulf­like

　　解析：选B　农民可以平整田地，使它们像梯级一样。stair­like"像梯级的"。

　　16．A.period B．century

　　C．history D．dynasty

　　解析：选B　at the beginning of the century"在本世纪初"。

　　17．A.thousand B．thousands

　　C．million D．millions

　　解析：选C　thousand, million等与具体数字连用时，不加­s，故排除B、D两项，根据常识可知选C。

　　18．A.affect B．use

　　C．save D．share

　　解析：选C　我们现在应该"节约(save)"每一寸土地。

　　19．A.Otherwise B．However

　　C．Therefore D．Though

　　解析：选A　otherwise"否则"，符合语境。

　　20．A.people B．globe

　　C．population D．number

　　解析：选C　用large修饰population，指人口多。

Ⅱ.阅读理解

　　Self­driving cars might make your future travel a lot more pleasant, but they won't reduce (缓解) traffic.

　　Car producers have mentioned that traffic reduction is one of the many advantages of having self­driving cars on the road. The idea is that self­driving cars will reduce accidents caused by human mistakes. But experts say self­driving cars' influence on traffic will probably be bad.

　　Lew Fulton, a co­director at UC Davis' Institute of Transportation Studies (ITS), said that self­driving cars won't fix traffic problems unless a pricing system is put in place that discourages self­driving cars. For example, many companies are interested in programming self­driving cars to do something, which could increase traffic on the road, Fulton said.

　　Massachusetts lawmakers have already suggested introducing a tax (税) on driverless cars. It calls for at least $0.025 per mile.

Traffic jams (堵塞) could also worsen as companies like Lucid Motors try to produce