21.In recent years global warming has become concern for people all over the world.
Tom was about to close the windows ______ his attention was caught by a bird.
By the end of this month, we surely _________ a good solution to the problem.
Now that she is out of a job, Lucy ________ going back to school, but she hasn’t decided yet.
On hearing the ________ result, all the students of Class Two couldn’t help _______.
Tom, I can’t see the notice clearly. May I _______ the seat ________ you?