What’s the matter, Mary? You looked upset.— I failed again in my math exam. I’m really sorry because I don’t want to ____ my parents down.

_________ others whenever you can _______you will feel happy.

_____ homework, most students do it every day.[ ]

The Internet is a wonderful discovery,________of great significance to people’s lives.

Is this _______ watch, Lily?— Yes, my father bought it for me yesterday.