— Susan, would you like to go hiking with us this afternoon?— I'd love to, but I study for a test.A. may B. have to C. can
—________she________doing her homework yet? —Yes,she has.She________it just now.
She has been in the city________.
Why don’t we consider________the Great Wall next weekend?
That clever boy regards the problems________challenges.
There are________people leaving the countryside to search________work in the city.