21. ––Has ______ problem been solved?
––Not yet. We’re trying to think of ______ way out, but it’s quite difficult to find one.
A. a; the B. the; a C. a; a D. the; the
22. While studying, fix your mind on what is really important, or you will _____ remembering nothing．
A．show up B．take up C. bring up D．end up
