A number of military personnel who served in Operation Desert Storm has encountered a series of unexplainable symptoms that were attributed to Gulf War syndrome.

A. has encountered a series of unexplainable symptoms that were attributed to
B. has unexplainably encountered a series of symptoms that have been attributed as
C. have encountered a series of unexplained symptoms that have been attributed as
D. have encountered a series of unexplainable symptoms that have been attributed to
E. have encountered unexplainably a series of symptoms that were attributed as


OA D

Source: Princeton Review