I'm looking for the wallet __________ I lost yesterday.[ ]
A. that
B. who
C. what
D. this
答案:A
变应性鼻炎最主要的病因是()
A.过敏体质
B.鼻腔感染
C.体内有慢性病灶
D.感冒
E.环境因素
简述浓缩的基本原理