_____ got into the room ______ the telephone rang.[    ]

A. He hardly had; then    

B. Hardly had he; when      

C. He had not; than      

D. Nor had he; when

人们常说的四大常规能源是指煤炭、石油（包括天然气）、水力与核能，而节能被认为是与四大常规能源并列的第五大能源。