be interested on后加什么？

　　Just out of interest, how much did it cost?

　　我只是好奇問問，這個花了你多少錢？

　　By that time I had lost interest in the idea.

　　那時我已經對此想法失去興趣了。

　　Could I interest you in this model, Sir?

　　先生，請你瞧瞧這個型號好嗎？