No one knows who cheated in the exam.
Do you know who broke the antique vase?
She could marry who she likes.
Who is not here now should report your reasons later.
He is no longer who he was.
I don't know what he is doing.
I'll do what I can do to help you.
What you sent me are useful.
This is what they call Silicon.
What hit me just now is still a mystery.