The possible long-term health risks to airline personnel who repeatedly cross multiple time zones has been a concern since the first jet transports went into service in the 1950s.

A) who repeatedly cross multiple time zones has been a concern since the first jet transports went
B) who are repeatedly crossing multiple time zones has been a concern since the first jet transports that went
C) who repeatedly cross multiple time zones have been a concern since the first jet transports went
D) repeatedly crossing multiple time zones has been a concern since the first jet transports went
E) repeatedly crossing multiple timezones have been a concern since the first jet transports going


OA C

Source: GMAT Prep