A beam of light will not bend round corners unless______to do so with the help of a reflecting device . 

This church is as old as, if _____ than, that one.

So absorbed          in our talk that my brother took a wrong turn on the way to the airport.

一Oh, poor Peter looks very weak.一＿if you suffer from a high fever for three days on end.

Look, _____ fashionable clothes is she wearing that all the eyes are fixed on her!