---Do you know when Dr Smith_____for dinner this evening?----No,but I think he _____when he is free.
I like English, ____ I am not good at it.
There is ____ office on _____first floor.
A: Is the pen on the desk? B: ____.
A: Is there a computer in your class? B: ____.
A: ____ boys and girls are there in your class? B: There’re21 boys and20 girls.