选矿效率，又称（）。在选矿过程中精矿里有用矿物或金属的增长量与设想的最佳条件下增长量之比。
参考答案：分选效率
特种设备在（），特种设备使用单位应当向直辖市或者设区的市的特种设备安全监督管理部门登记。
A.投入使用前或使用后30日内
B.一年后
C.保修期后
Which of the following statements is true according to what you have heard
A．I will eat lunch very quickly.
B．I will have lunch before the meeting.
C．I will eat lunch at the meeting.
D．I will eat lunch while jogging.
