Man cannot go on increasing his number at the present rate. In the (56) 30 years man will face a period of crisis. (57) experts believe that there will be a widespread food (58) . Other experts think this is (59) pessimistic (悲观的), and that man can prevent things from (60) .

(61) thing that man can do is to limit the (62) of babies born. The need (63) this is obvious, but it is not (64) to achieve. People have to be (65) to limit their families. In the countries of the population (66) , many people like big families. The parents think that this (67) a bigger income for the family and ensures there will be someone in the family who will look (68) them in old age.

Several governments have (69) birth control policies in recent years. (70) them are Japan, China, India and Egypt. In some (71) the results have not been successful. Japan has been an (72) . The Japanese adopted a birth control policy in 1948. People were (73) to limit their families. The birth (74) fell from 34.3 per thousand per year to about 17.0 per year (75) present.

57（）

A．Any

B．Some

C．More

D．All

外部防雷系统由避雷针（或避雷带、避雷网）、引下线和（）等构成。

A、接地桩

B、等电位

C、接地系统

D、避雷器