钢管水浸法聚焦法探伤时，下面有关线聚焦方式的叙述中，哪条是正_爱下问搜题

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问题单项选择题

钢管水浸法聚焦法探伤时，下面有关线聚焦方式的叙述中，哪条是正确的？（）

A.探伤速度较快

B.回波幅度随缺陷长度增大而增高

C.聚焦方法一般采用圆柱面透镜或瓦片型镜片

D.以上全部

答案

参考答案：D

完形填空

选择下列各句，填入短文中的空白处，使短文意思完整。

A. The United States is the only industrial country whose population is increasing
B. And a fifth go without modern health services
C. Asia has more than doubled its population since 1960
D. Most of the growth is taking place in Africa
E. Now some 6 billion mouths must be fed and bodies clothed and housed

Every year there are about 95 million more people on the earth. (66) ___and parts of South and west Asia that can hardly afford more people. However, population increases have slowed or even stopped in Europe, North America and Japan.
By 1960, about 70 percent of the world’s people lived in developing countries. Today it is 80 percent, and 95 percent of the world’s population growth is taking place in these countries.(67)____, as have Latin America and the Caribbean area. North America’s population has grown by a half, while Europe’s has risen by only 20 percent and is now stable. (68) ______-- not because of birth, but of the coming of people from the rest of the world.
In 8,000 BC, only 5 million people were alive. (69)_____.To meet those needs humans are using lots of things on the earth in a wrong way -- for example, cutting down too many trees and catching too many fish. These wrong doings are dangerous for human life and health around the world.
At the beginning of the 21st century, nearly 60 percent of 4.8 billion people in developing countries have no basic sanitation. Almost a third don’t have enough clean water. A quarter don’t have enough housing. (70)_______.

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