sometimes后面加什么形态

　　Sometimes I go by car.

　　有时我坐车去。

　　Sometimes I pay, sometimes he pays ─ it seems to average out.

　　有时我付钱，有时他付钱——看来两相持平。

　　Our jobs overlap slightly, which sometimes causes difficulties.

　　我们的工作略有重叠，所以有时引起一些困难。

　　Sometimes small firms can outdo big business when it comes to customer care.

　　在顾客服务方面，有时小企业可能优于大企业。

　　Mothers who are depressed sometimes fail to bond with their children.

　　患忧郁症的母亲有时无法和孩子建立亲子关系。