First of,the idea of having liberty and independence of their own ethnic race has spread to the colonies guring WWII,this caused the uprising of protests and unrest of colonies which shook the colonial rulers.
Also,after WWII,the European Nations were greatly damaged,as the war destryoed infrastructures and killed civilians,they faced the problems such as lack of labour,unemployment and hyperinflation. The nations were busy to settle the unrest and recovery within the nation and could not spare resources to maintain their colonies
The American attitude shifted in favor of rights for Native Americans. This is based on "Polls showed that Americans believed in rights for Native Americans". Why it's not A is because it wasn't the polling that contributed to the act, but what the polls showed which is C.
