--Have you seen Jack? His mother is looking for him all the afternoon.--No, I haven’t. I am sure his mother________be very worried.
It’s a good idea _____ a pen friend to practise English.
How many ______ medicine are used for the children of six years old?
Eating fruit and vegetables can help you ______ more vitamins.
Here ______ in the classroom.
We should keep our classroom ______.