4.The reason energy and water sit at the top, ahead of food and poverty, is that addressing them makes subsequent problems easier to deal with. (Para. 5)

A. Energy and water are the top two problems on the list. The reason is that if we start to solve these problems, the other problems that follow them on the list, such as food and poverty, will be easier to deal with.
B. Energy and water are listed as the two problems more important than food and poverty. This is because once we start working on them, addressing food shortage and poverty will be easier later on.