Answer:
The dirtier I get, the whiter I am. What am I?
I begin your sentences.
I help engines spin and pants stay up. What am I?
I am an instrument that you can hear but cannot see or touch. What am I?
Die without me, never thank me. Walk right through me, never feel me. Always watching, never speaking. Always lurking, never seen. What am I?
The answer I give is yes, but what I mean is no. What was the question?