We must find a dictionary. ____ will do.

This project requires close teamwork.   Will be achieved unless we work well together.

—Shall I attend my friend's coming­of­age ceremony, Mum?—No, unless you see to ________ that you will be home before 10：00 P．M.

The two girls are so alike that strangers find ____ difficult to tell one from the other.

I was blessed with a happy childhood, _____ most people would want to have.