建立一项应急补助或储备是应对已知风险最常用的风险()措施。A．转移 B．缓解 C．接

影响患者角色适应的因素有()

A．疾病的性质和严重程度

B．症状的可见性

C．人际关系的舒适感

D．医院规则

E．患者的社会特征

下列哪种外加剂适用于大体积和夏季施工混凝土（）。

A.氯化钙

B.氯化铁

C.糖蜜

D.三乙醇胺

影响公司流动比率的主要因素有( )。

A．净资产

B．营业周期

C．流动资产中的应收账款

D．存货的周转速度

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.

5（）

A.history 

B.shortcoming 

C.achievement 

D.advantage