. We’d like to do _______ we can _________ the poor.

As a teacher, I seldom give my students so difficult a problem_______ they can’t work out.

There is a new problem involved in the popularity of private cars _______ road conditions need _______. 

 Great changes have taken place in that factory. It is no longer _________ it was 20 years ago,_____ it was so poorly equipped.

 —Tom has passed the final exam.—______! He never really worked hard before.