我们将设备故障发展变化的规律概括为（）。
A.三段理论
B.寿命周期理论
C.经济劣化理论
D.澡盆理论
参考答案：B
The father as well as his daughters _____ skating on the freezing river every Sunday afternoon.
A．go
B．goes
C．is going
D．are going
