I was doing my homework _______ mother was cooking.

–_______________ does a CRH train run? –It runs up to more than 300 km an hour. 

--- Mr. Green, I think physics is too difficult for me. ---Tom, work hard, _______ you’ll find it not as difficult.

You’ll fail your next English exam _______ you work harder from now on.

 —Did you have a good time at the party?—Yes. We sang ______danced until late at night.