1.
He
is looking for the book which he lost. Is
he looking for the book which he lost?
He isn`t looking for the book which he lost.
2.
The
sky is getting very dark. Is the sky getting
very dark? The sky isn`t getting very
dark.
3.
They
are laughing at what you said. Are they laughing at what you said? They aren`t
laughing at what you said.