21. Smith wants to be ______ engineer while Mary wants to be ______ teacher.
A. an; the B. the; the C. an; a D. the; a
22. The baby was born with a heart problem and only ______ for a few hours.
A. survived B. stayed C. escaped D. recovered
23. Ningbo is such a beautiful city that it is well worth ______.
A. visit B. visiting C. visited D. to visit
