单选题 The Food and Drug Administration classifies as a cosmetic any product whose ______ purpose is to improve a person's appearance.
A. singular B. sincere
C. single D. significant

【正确答案】 C

【答案解析】[解析] single purpose“单一的目的”，指only one; singular“单数的”，singular还有“非凡的，卓越的”的意思，a woman of singular beauty“绝美女子”；sincere“真诚的”，习惯上不用来修饰purpose；significant“重要的”，通常也不与purpose搭配使用。