Usually pilots need about a decade of experience they can be promoted to captain.
A. after
B. before
C. then
D. when
网友回答
A. after
(答案→)B. before
C. then
D. when
解析：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。