直顶式液压电梯可以不设置安全钳，但必须在液压缸的油口装设限速切断阀。()
参考答案：对
Of all the subjects, chemistry seems to be for me.
A．difficult
B．too difficult
C．more difficult
D．the most difficult
细胞外液主要阳离子是
A．钾离子B．钠离子C．钙离子D．镁离子E．氢离子
