脱落细胞检查背景成分不包括（）
A.黏液
B.异物
C.上皮细胞
D.红细胞
E.坏死物
参考答案：C
— wants to learn a new song? — I want.[ ]
A. Who
B. When
C. What's
Occasions are quite rare ________ I have the time to spend a day with my kids.[ ]
A. who
B. which
C. why
D. when
