This is the most interesting book ______ I have ever read.
Xi’an is one of ______ capital ______ in China.
If we keep planting trees, our country will become ______.
— do your parents go to the movies? —Once a month.
Only ten boys in our class use the Internet to get information, ______ use it to play games.
— When did he go to summer camp?— He _____ to summer camp five days _____.