下列现象中哪一个不是锅炉缺水事故的现象()
A.水位报警器发出低水位警报
B.水位表内看不到水位,表内发白发亮
C.过热蒸汽温度下降
D.锅炉排烟温度上升
参考答案:C
We ______ here for three years. [ ]
A. have been
B. have come
C. have came
D. came
羊水过少的定义是足月妊娠时,羊水量少于
A.300ml
B.400ml
C.500ml
D.800ml
E.1000ml