could和should的區(qū)別：

1. should可以用于第一人稱或第三人稱的疑問句中，表示征求意見。

例如： My brother likes to listen to CDs. He often plays his CDs too loud. What should I do?

2. should 表示義務(wù)，可以用于提供建議，表示“應(yīng)該”, 后面跟動詞原形。

例如： Maria argued with her mother last night. She is very upset now. What should she do? I think she should say sorry to her mother.

3. should也用于表示某事發(fā)生的可能性，用于表示推測的詞，意為“可能”。

例如： They should arrive soon.

4. could不僅僅是充當can的過去式，而且是一個單獨的情態(tài)動詞，表示“能；可以”，用來提供建議，后面跟動詞原形，它和should在意義上不同，前者是“可以”，后者是“應(yīng)該”，表示不同的態(tài)度，但兩個都可以用來提供建議。

例如： You could borrow a bike to that park. I think you should have a talk with your friend.