Choose the correct answer that complete these given words.

Laser / device / concentrate / light waves / intense beam.

A. would be 

B. was  

C. had been  

D. were

A. degree

B. certificate

C. diploma

D. qualification

A. enthusiasm

B. experience

C. certificate

D. concentrate

A. they keep the users alert all the time.

B. they are indispensable in everyday communications.

C. they make them look more stylish.

D. they cannot be replaced by regular phones.

A. Unless I knew it was my friend, I would not answer the door.

B. I knew it was my friend, but I did not answer the door.

C. Only when I answered the door did I knew it was my friend.

D. I answered the door since I knew it was my friend.

A. which

B. what

C. when 

D. where