近年来，长江洪灾频繁发生，其主要自然原因是                       （    ）
①中游地区围湖造田
②中、下游地势低平
③流域内降水丰富
④上、中游砍伐森林破坏了植被
⑤支流众多，雨季涨水集中

已知点A（﹣1，1），B（﹣4，5），若$\overrightarrow{BC}$=3$\overrightarrow{BA}$，则点C的坐标为（　　）

    Dan and Kim are friends. Dan lives in an apartment downtown(市中心). It is very convenient to go to work or go shopping, but it's too noisy. There is a lot of traffic. Sometimes Dan can't stand(忍受). Kim has a house in the suburbs(郊区). It's not convenient to go to work or go shopping, but it's very quiet. There is not much to do. In fact, nothing ever happens.

    Dan and Kim have a good idea. They decide to trade(决定交换)places one week.