The scientist does not study nature ________ it is useful to do so. He studies it because he takes pleasure in it.

How long have they ____________ Shanghai —About a week.

Why weren’t you at school yesterday morning,Li Lei? —_________,sir

Did you find the answer_____ the question about _____ TV very interesting

I do not usually celebrate my birthdays until I met him_______, I do not like any big party because I’m not good at small talk