每一提升装置，必须装有从井底信号工发给井口信号工和井口信号工发给绞车司机的（）。
A、闭锁装置
B、信号装置
C、通风装置
参考答案：B
The equation relates the values of two linked currencies, where R is the value in dollars of one currency and S is the value in dollars of the other currency. Which of the following equations can be used to convert dollar values from the R currency to the S currency ？（）
A.A
B.B
C.C
D.D
E.E
爆破员在运送火药过程中注意哪些事项？
relates the values of two linked currencies, where R is the value in dollars of one currency and S is the value in dollars of the other currency. Which of the following equations can be used to convert dollar values from the R currency to the S currency ？（）