I recorded the professor’s speech on my cellphone _____ I could listen to it several times later.

The area ______ the explosion happened was closed off by the police.

Use your head, _______ you’ll work out the problem.

_______ is known to all, Lu Xun was famous as a great thinker.

It’s the first time ______ he has helped us. 

No one knows exactly ______ this important discovery was made.

I think you should end it _______ it’s too late, or you may be sorry about it later.

----What a beautiful picture!
----It’s years ______ I painted a picture as beautiful as this one.

“It’s a secret. Promise no one else would know it”, he lowered his voice and whispered ____ no one could overhear it.

She was moving out of her old apartment _______ she suddenly realized that the key to the new apartment wasn’t on her.