Who among the living could know the true source of his life?

He felt blue and did not know the source of it.

They would have given their right hands to know the source of it.

Even before I had turned completely, though, knew the source of the sound.

Still, he felt the edge of fear within him and knew its source.

And you've got to know the source of your funds to do it.

"I should be most curious to know the source of such a story."

You do not know the source or cause of your anxiety.

I, for one, wonder if we already know her source.

She made a noise that I didn't really want to know the source of.