甲、乙、丙三瓶奶分别加入乳酸菌后，甲乙两瓶密封，丙瓶敞开。甲瓶加热到100℃后再冷却，然后均在室温下放置12小时，可以变成酸奶的是 [ ]

A．甲

B．乙

C．丙

D．甲和乙

When you are firing a pyrotechnic distress signal，it should be aimed（）.

A.horizontally and directly abeam of your vessel

B.at the vessel whose attention you want to attract

C.into the wind

D.at greater than 60 degrees above the horizon