--- Why does she leave a key to you?
--- , I think.
A. In convenience
B. For convenience
C. With convenience
D. At convenience
网友回答
A. In convenience
(答案→)B. For convenience
C. With convenience
D. At convenience
解析：考查情景交际。句意：--她为什么给你留下一把钥匙？--为了方便，我认为。for convenience为了方便起见。故选B。