血尿是指离心后的尿液在显微镜下每高倍视野红细胞数超过（）

A.1个

B.2个

C.3个

D.4个

E.5个

If x, y, and z are positive integers and x²=y²+z², which of the following must be true ？（）
Ⅰ.x＞z
Ⅱ.x=y+z
Ⅲ. y²+z² is a positive integer

A. Ⅰ only

B. Ⅱ only

C. Ⅲ only

D. Ⅰ and Ⅱ only

E. Ⅰ and Ⅲ only