Which of the Following Best Describes the Role of Foederati

Which of the following best describes the role of foederati in the later western Roman Empire?

A) They were useful as military allies in the short term,but contributed to the fall of the empire in the long run.
B) They were savage barbarians who undermined Roman culture.
C) By introducing Islam to the West,they hastened the fall of the empire.
D) They strengthened the empire economically but had little military impact.
E) Roman emperors took advantage of the foederati's weak leaders.