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:B
----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
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