David wants to be engineer while Cathy wants to be doctor.A. an; theB. the ; theC. an; a

问题补充：

David wants to be engineer while Cathy wants to be doctor.

A. an; the

B. the ; the

C. an; a

D. the;

答案：

A. an; the

B. the ; the

(答案→)C. an; a

D. the;

解析：考查冠词。本题使用不定冠词a/an+单数名词泛指一类职业.句意：David想做工程师，而Cathy想做医生。故C正确。