Across the street, the parking lot of Haiti's elite police emergency response unit has become an open-air medical clinic.

VOA: standard.2010.01.26

you could leave your response to the invitation slightly open-ended by saying you're not sure.

你可以表示你不确定，开放性地回复这个邀请。

I don't know 课堂 - SpeakingMax英语口语达人