Much of the Research That Has Been Done on Intercepted

Much of the research that has been done on intercepted or failed suicide bombers

A) is difficult to carry out because they are immediately executed by the governments that capture them, if they manage to escape the death squads of their own group.
B) is useful because failed suicide bombers and successful ones are the same.
C) uses very small samples.
D) uses only the terrorists that weren't killing for religious reasons.