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问题 选择题

等腰三角形的一个外角是100。，则其底角是[ ]

A.80°或20°

B.80°或50°

C.80°

D.50°

答案

答案：B

选择题
Scientists overcame (克服) much difficulty they had _____ that technological problem _____ they finally could send the manned (载人的) spaceship up into space.
A. to solve; until
B. solving; before
C. to solve; before
D. solving; until
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单项选择题

A类火灾是指（）。

A、固体物质火灾

B、气体火灾

C、金属火灾

D、液体火灾
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