Please be careful in the lab, ________ you?

A．will

B．won't

C．don't

D．do

When the second class began, I ________ that I had left my book in the lab．

A．have known

B．realize

C．have realized

D．realized

We ________ to close the windows before we left the lab．

A．tell

B．told

C．are told

D．were told