How was vietnam able to become and remain autonomous despite china's power and dynamism?

Throughout history, Vietnam was not totally free from China’s power and dynamism, having been under Chinese domination for different, interrupted time periods, the earliest being in 111 BC. Being a strategic southern territory, the Chinese used now-Vietnamese territory to launch expeditions to Southeast Asian states. The last Chinese occupation of Vietnam ended in 1427, with the Chinese Ming Dynasty accepting Vietnam as an independent, yet tributary state. 

the answer would be:

b. race

answer: i looked it up

explanation: in 1955 in montgomery, alabama, a girl refused to give up her seat on a public bus. the girl was black, and the passenger looking to take her seat was white. this is a familiar tale, but it's not about rosa parks. the girl in the story is a 15-year-old high school student named claudette colvin, and this act of defiance occurred nine months before rosa parks did the same thing. colvin was arrested, and her case is what led to the u.s. supreme court's order for the desegregation of alabama's bus system. so, why don't we know colvin's name? "later i had a child born out of wedlock; i became pregnant when i was 16," colvin says. "and i didn't fit the image either, of, you know, someone they would want to show off.