Jerry is _________ today. He needs to clean the blackboard and the classroom.
A.on duty B.on fire C.on business D.on sale
This is the best thing you've ever done. I'm so happy f________ you.
Please don't drink plenty of cold water a________ doing sports. It's bad for your health.
Don't worry. The next car will come i________ 5 minutes.
If you want to interview the famous star, I think you need to learn more a________ him.
More and more people choose to go to work b________ subway. It's convenient and fast.
