(2013 ·湖北武汉武昌高三联考)Smiling doesn't ________ mean you're happy.Sometimes, it just means that you're strong enough to face problems.

A．fortunately

B．eventually

C．deliberately

D．necessarily

某中间站牵出线有效长370m，以11m为换算单位计算，机车长度是24m，其最大换算容车数是（）。