Army schools in Germany provide a useful source of singers.

Some of these personal accounts are highly useful historical sources.

The local nurse had been coming in to see her and she might be a useful source of information.

The intelligence test can be a useful source of evidence about individuals who are considered for lower level jobs.

"He has been a very useful intellectual source for Bill and probably always will be."

But I'm the most useful source of information you're going to be able to find here, now or at any other time.

They said the man had become a "useful source of information," but declined to provide his name or say where he was being held.

This could well be a useful source of information on local educational research.

Your employees can be a very useful source of ideas.

It promised to be a most useful source of information.