✔ 最佳答案
To make it simple, the problem now is "water crisis" due to population growth. The solution is to propose some strategies (usually in a list) and we need to choose the best among them.
Case 1: If you are the one who need to propose some strategies, then you need to explain WHY it is the best approach to solve the problem. For example, the cost of your strategy is cheaper.
Case 2: Otherwise, if some existing strategies are listed, then you only need to evaluate them one by one and choose the best approach among them. Of course, you still need to give reasons why you think one of them is the best.