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【单选题】

To use it seems so natural to put up an umbrella to keep the water off when it rains. But actually the umbrella was not invented as protection against rain. Its first use was as a shade against the sun!
Nobody knows who first invented it, but the umbrella was used in very ancient times. Probably the first to use it were the Chinese, way back in the elh century.
We know that the umbrella was used in ancient Egypt and Babylon as a sunshade. And there was a strange thing connected with its use: it became a symbol of honor and authority. In the Far East in ancient times, the umbrella was allowed to be used only by royalty or by those in high office.
In Europe, the Greeks were the first to use the umbrella as a sunshade. And the umbrella was in common use in ancient Greece. But it is believed that the first persons in Europe to use the umbrella as protection against the rain were the ancient Romans.
During the Middle Age, the use of the umbrella practically disappeared. Then it appeared again in Italy in the late sixth century. And again it was considered a symbol of power and authority. By 1680, the umbrella appeared in France, and later on in England.
By the eighth century, the umbrella was used against rain throughout most of Europe. Umbrellas have not changed much in style during all this time, though they have become much lighter. It wasn’t until the twentieth century that women’s umbrellas began to be made, in a whole variety of colors. Which of the following statements is not true about the umbrella

A.
No one exactly knows who the inventor of the umbrella was.
B.
The umbrella was first invented to be used as protection against the sun.
C.
The umbrella changed much in the eighth century.
D.
In Europe, the Greeks were the first to use the umbrella.
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【单选题】复合固定桥包括的牙单位一般为

A.
2个或2个以上
B.
3个或3个以上
C.
4个或4个以上
D.
1个或1个以上
E.
5个或5个以上

【多选题】下列说法中正确的是 。

A.
冻土层的平均冻胀率为地表冻胀量与冻层厚度的比值
B.
冻土层的平均冻胀率为地表冻胀量与设计冻深的比值
C.
设计冻深为冻层厚度与地表冻胀量之差值
D.
设计冻深为冻层厚度与基础底面允许残留冻土层厚度之差值

【单选题】在桥基内由屈应力所产生的力矩反应称

A.
挠曲变形
B.
内压力
C.
外张力
D.
曲矩
E.
屈应力反应