In accordance with SOLAS， the batteries that power interior lighting in inflatable liferafts can be made to last longer by（）.

In accordance with SOLAS， the batteries that power interior lighting in inflatable liferafts can be made to last longer by（）.
A.unscrewing the bulb during the daylight
B.switching the light on only when necessary
C.taking no action as there is no way on saving power
正确答案：switching the light on only when necessary