We can talk with friends on the Internet _______ it’s easier and cheaper.
We are happy_______ you to the party for our friends from Beijing.
After reading for an hour, you'd better_______ the green trees for a minute or two.
Do you need help _______ your Maths homework?
Which floor do you_______ this tall building?
-How many students are there in your school?-There are about eight_______ students.