单项选择题
What kind of products do the air carriers deliver? （）
A. The high value B. Low density or weight C. A and B D. To add cost
单项选择题 （）is the disadvantage for air transportation?
单项选择题 What is the meaning of “short hauls”? （）
单项选择题 Motor transport has the biggest market share in the paragraph. Is it true or not （）
