Are you willing to live on Mars（火星） one day— ______________ It sounds exciting, but it still worries me.

There is _____ “s” and _____ “u” in ______ word “use”.

I’m sorry that what I said just now has hurt you, but I didn’t do it _____

Great changes _____ in my hometown in the last 30 years and local people are living a happy life today.

class, the student leaders are on______ duty every ______ few days.