Which transportation development had the greatest long-term impact on the american economy?

the policy of appeasement influenced the beginning of ww2 because hitler gave the other countrys chocies but after they choose to try and appease hitler to not invade their country but he still invaded them.

the answer is d because for c the actors can't love acting for the other's audience their not even in the same show, it can't be b either because the question is talking about the actors not the audience, and it can't be a because   it's not specific enough