练习题考试资料

Scientists at Sussex University appear to be on the way to ___1___ how the mosquito, carrier of diseases such as malaria and yellow fever, homes in on its target. The problem is that they have found t...

The difference between a liquid and a gas is obvious under the conditions of temperature and pressure commonly found at the surface of the Earth. A liquid can be kept in an open container and fill it ...

Homing pigeons are placed in a training program from about the time they are twenty-eight days of age. They are taught to enter the cage through a trap and to exercise above and around the loft(鸽棚...

Plastics are materials which are softened by heat and set into lasting form when shaped in a mold. Some are natural; some are semi-synthetic(半合成的) , the result of chemical action on natural su...

In today's world, insurance plays a vital role in the economic and social welfare of the entire population. The wish to guard against dangers to life and property is basic to human nature. By using va...

During the nineteenth and twentieth centuries, migrations have taken place within__1__ countries; the cities with their industries have attracted people away from the country. The possibility of earni...

Laziness is a sin(罪), everyone knows that. We have probably all had lectures pointing out that laziness is immoral, that it is wasteful, and that lazy people will never amount to anything in life. B...

What do we think with? Only the brain? Hardly. The brain is like a telephone exchange. It is the switchboard, but not the whole system. Its function is to receive incoming signals, make proper connect...

Like most parents, geologist Brain Atwater worries about his daughter's safety. But these days, he has an unusual concern; The public school she___1___ in Seattle has unreinforced brick walls, a ___2_...

Every day 25 million U. S. children ride school buses. The safety record for these buses is much better than for passenger cars; but nevertheless, about 10 children are killed each year riding on larg...