题目

 I _______ keep dogs for protection, but now I keep them as pets.   A. would rather      B. had better          C. used to                D. have to 答案：C原尿与血浆的成分相比较，原尿中不具有的成分是 A.无机盐                                B.葡萄糖 C.大分子蛋白质                          D.尿素