单项选择题
Where is the most air freight shipped in the passenger aircraft?（）
A.Separately B.In same level C.In the lower part D.Not mention here
单项选择题 How much is the percent of air transportation in all modes?（）
单项选择题 What kind of products do the air carriers deliver? （）
单项选择题 What is the disadvantage for air transportation?（）
