Answer:
The right answer here is a.
a. of pressure put on them by the westward migration of the Huns.
Explanation:
The Germanic tribes had a long, several-century history of conflict and interaction with the Romans. In the 4th century CE, hosts of a ferocious Asian nomad people, the Huns, were on the move from the east. They crossed the Volga river, attacked and vanquished the Ostrogoths in Eastern Europe. The Visigoths implored the Romans for sanctuary within the limits of the empire.
