问题补充：
writer, she is excellent, teacher she is not very good.
A. As; but as
B. As; and as
C. As a ; but as a
D. As a; and as a
答案：
A. As; but as
B. As; and as
(答案→)C. As a ; but as a
D. As a; and as a
解析：作为一个作家，她是优秀的；但作为一名教师，她就不是很好的了。 writer 和teacher都是可数名词，单数要加冠词a。
