During the war three nations fought _____ the island as an airport. [ ]

A. for controlling and using

B. to control and using

C. controlling and using

D. to control and use

交流电是指电流的

A．方向不随时间而改变的电流
B．方向随强度而改变的电流
C．方向不随强度改变的电流
D．强度随方向改变的电流
E．方向和强度不断地随时间而改变的电流