在紫外光下，欧盟旗帜上的12颗星由（）色均变为（）色。

A、蓝 

B、黄 

C、绿 

D、橙

How should signal flares be used after you have abandoned ship and are adrift in a liferaft?（）.

A.Immediately use all the signals at once

B.Use all the signals during the first night

C.Employ a signal every hour after abandoning ship until they are gone

D.Use them only when you are aware of a ship or plane in the area