重庆市某天的最高气温是17℃，最低气温是5℃，那么当天的最大温差是（    ）℃。

On a vessel，if someone fell overboard and you did not know over which side the person fell，you should（）.

A.immediately reverse the engines

B.stop the propellers from turning and throw a ring buoy over the side

C.increase speed to full to get the vessel away from the person

D.first put the rudder hard over in either direction