下列图形中：①平行四边形；②有一个角是30°的直角三角形；③长

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问题选择题

下列图形中：①平行四边形；②有一个角是30°的直角三角形；③长方形；④等腰三角形。其中是轴对称图形有几个 [ ]

A．1个

B．2个

C．3个

D．4个

答案

答案：B

选择题

----This returned Chinese scholar has become one of the top experts in this field.

----Yes,I know him very well.He____in Africa with animals for eight years.

A．has worke

B．had worked

C．worked

D．has been working

单项选择题

要使加热炉燃料完全燃烧，特别要控制（）、灰分等杂质不能过多。

A、轻组分

B、水分

C、蒸汽

D、天然气