Basically, the US wanted access to the Panama Canal, and since the Canal wasn't yet built, it needed to built it. Originally the US made an proposal (which wasn't yet questionable), but Columbia (at the time Panama was part of Colombia) wasn't comfortable with the proposal, and the US decided to enforce their plan in other ways, so that they still gain access to the canal.
Answer:
Emigrants feared death from a variety of causes along the trail: lack of food or water; Indian attacks; accidents or rattlesnake bites were a few. But the number one killer, by a wide margin, was disease. The most dangerous diseases were those spread by poor sanitary conditions and personal contact.
Explanation:
Your answer would be C) Coastal Plains because the area is humid and has hot summers and cool winters, without any hard freezes, which won't drastically affect the growth of crops.
Hope this helps. If I'm right or wrong, please let me know :)