Answer:
1) Odoacer used his popularity with his troops to overthrow the emperor.
Explanation:
In the words of J. B. Bury, "[The <em>foederati</em> desired to have roof-trees and lands of their own, and they petitioned Orestes to reward them for their services, by granting them lands and settling them permanently in Italy". Orestes refused their petition, and they turned to Odoacer to lead their revolt against Orestes. Orestes was killed at Placentia along with his brother Paulus outside Ravenna. The Germanic <em>foederati</em>, the Scirians, and the Heruli, as well as a large segment of the Italic Roman army, then proclaimed Odoacer <em>rex Italiae </em>("king of Italy"). In 476 Odoacer advanced to Ravenna and captured the city, compelling the young emperor Romulus to abdicate on 4 September.
Saying that, Odoacer didn't assassinate Romulus, nor did he start a long and bitter civil war.
Choice 3 doesn't say anything about overthrow so that one is also out, leaving Choice 1 as the answer to this very thoughtful question.
