An ad hoc committee = a committee set up to study a particular problem.

专门委员会（为研究某一专门问题成立起来的委员会）

Ambassador MacKay of again assumed the Chair of the Ad Hoc Committee.

麦凯大使的再次担任主席的特设委员会.

Eg:This is an ad hoc committee specially established to deal with a particular subject.

这是一家专门成立的处理某一问题的特别委员会。

He at once appointed an ad hoc committee on blood and blood derivatives to serve in an advisory capacity to him.

他也立即成立一个血液与血液衍生品方面的特别委员会作为他的顾问团。

The Ad Hoc Committee has now completed its Final Report and has submitted it to the Task Force on University Governance of the Council for consideration.

专责委员会现已完成最后报告， 并呈交大学校董会属下的大学管治专责小组考虑。