诊断急性白血病，外周血哪项异常最有意义（）

A.白细胞计数2×10⁹／L

B.白细胞计数20×10⁹／L

C.原始细胞27％

D.分叶核粒细胞＞89％

E.中性粒细胞90％

Science is more than a collection of unrelated facts; to be meaningful and valuable, ______ must be arranged to show generalized character.

A．which

B．those

C．it

D．they