启动离心泵时,如果泵在额定流量内运转而电机超负荷时应立即停泵。
参考答案:对
When I stayed in the countryside I enjoyed _____ leisurely walk in the fields, and felt _____ warmth
of the sun on my face.[ ]
A. /; the
B. a; a
C. /; a
D. a; the
下列物质由离子构成的是( )
A.汞
B.氮气
C.氯化钠
D.二氧化碳