在肺泡表面活性物质的组成成分中，下列哪种物质含量最多
A．卵磷脂
B．鞘磷脂
C．中性脂肪
D．蛋白质
E．磷脂酰甘油
参考答案：A
—What do you think of the news in today's newspaper?
—We shouldn't ________ the trouble of helping others only because what we do may invite trouble.
A．knock off
B．take off
C．keep off
D．break off
简述变电所综合自动化的特点及优越性。
