臭氧层阻挡了太阳( )_的紫外线辐射，就像是地球的一把“保护_爱下问搜题

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问题单项选择题

臭氧层阻挡了太阳( )_的紫外线辐射，就像是地球的一把“保护伞”。( )

A．80%

B．89%

C．90%

D．99%

答案

参考答案：C

选择题

We ____ on the project for two hours. Let’s have a rest.

A. have been working
B. are working
C. worked
D. had worked

问答题简答题

说明如何区别木材的三切面