Question

Usually pilots need about a decade of experience _______ they can be promoted to captain.

A．after

B．before

C．then

D．when

Answer 1

B

试题分析：考查连词：A. after在…之后，B. before 在…前面，C. then那时，D. when当…时候，句意：通常，飞行员需要十年的经验才能被提升为机长。说明在被提升为机长前要十几年的时间。选B。