I think it's very useful. It may not be immediately apparent to people in Darfur, but in the end it is a contribution towards a solution to their problem."

VOA: standard.2009.10.23

On the other hand, you don't have to withhold information that may be useful to the class.

另一方面,你又不能刻意保留对这门课有用的信息

耶鲁公开课 - 基础物理课程节选

Some may or may not be useful, but you just don't know.

有些可能有用,有些可能没用,但你们现在还不知道

耶鲁公开课 - 基础物理课程节选