搜题请搜索小程序“爱下问搜题”
问题 选择题

地震波横波（S）和纵波（P）的传播速度在莫霍面处发生的显著变化是[ ]

A、S波、P波都明显增加

B、S波、P波都明显下降

C、S波完全消失，P波突然下降

D、P波完全消失，S波突然下降

答案

答案：A

单项选择题

选用补充概算定额“地下连续墙——深层水泥搅拌桩防渗墙——单头搅拌桩机”时，如墙厚为0.26m，人工定额乘以（）进行调整。

A.1.16

B.1

C.1.2

D.0.95
查看答案
单项选择题

It is clear that some chemicals can damage the health of animals and humans. (1) , this is not the only problem that (2) be caused by the careless use of chemicals. Chemicals can also (3) the ecological balance of the environment. If the ecological balance is disturbed, the results can be (4) serious.

The (5) of DDT illustrates the problem. DDT, a chemical which kills insects, at first seemed to be a perfect answer (6) many problems. It would control insects that caused dangerous diseases, (7) insects that caused billions of dollars of damage to crops every year. Governments permitted and even (8) the use of DDT. Farmers in many countries (9) to spray it on their crops. The (10) results were good: Damage to crops (11) down, and profits went up. However, the chemical had effects which the scientists didn’t see in (12) . First, it also killed insects which were the (13) enemies of the harmful insects and which were therefore beneficial to farmers. Second, and perhaps worse, DDT did not kill (14) harmful insect. A few insects had natural resistance to the chemical. They (15) and reproduced in large numbers. In a few years there were large numbers of insects which were not (16) by DDT, and there were (17) insects which could act as natural (18) on these new "super-insects". Finally, it became clear that DDT was not solving the insect problem. In fact, it was making the problem worse. It (19) became necessary to find a second (20) for the effects of the first.

13（）

A.natural 

B.ill 

C.ugly 

D.friendly
查看答案