keep后加什么形式

　　I'm sure she's keeping something back from us.

　　我肯定她有什么事瞒着我们。

　　Some teachers find it difficult to keep their classes in order.

　　有些教师觉得难以维持课堂秩序。

　　Keep down! You mustn't let anyone see you.

　　蹲下！一定不要让人看见你。

　　I keep thinking back to the day I arrived here.

　　我不断回想起刚到这儿那一天的情景。

　　Keep that dog out of my study!

　　别让那狗进我的书房！