单项选择题 （） transport of goods is the principal means of transport in many countries due to the low threshold infrastructure requirements.

多项选择题 Customs clearance in the import-export trade is one of the traditional functions of a freight forwarder.Customs clearance measures mainly include （）。

单项选择题 On traffic lanes where demand is strong and plane capacity is limited， the air rates will be （）and vice versa for traffic lanes where supply exceeds demand.