You are underway and pass by a lighthouse.

问题：

You are underway and pass by a lighthouse. Its light，which was white since you first sighted it，changes to red. This means（）.

A.the light is characterized as alternately flashing

B.the lighthouse has lost power and has switched to emergency lighting

C.it is the identifying light characteristic of the lighthouse

D.you have entered an area of shoal water or other hazard