我国水上无线电通信规则中规定，海上无线电话业务共分为（）种.
A、1
B、2
C、3
D、5
参考答案：C
我国选煤厂采用最广泛的选煤方法是重介选。
I was ______ in my reading, and didn't at first hear the doorbell ring.
A．immured
B．immersed
C．busy
D．infatuated
