Giving up smoking is a slow and painful _______ for him.

  In this experiment, the famous professor showed three different ________ to the study of physics.(2012·河北保定中学月考)

One hundred percent _______ to your studies, though it can be lonely and no fun at all, will leave precious marks on your youth.

 The children helped to carry their mother’s       from the shops.

 --- I’ll buy you a ten-speed bicycle as a birthday present.  --- Is that a _________?  I wish you would not disappoint me.