EPO不具有以下哪种功能（）

A.诱导血红蛋白的合成

B.促使幼红细胞提前脱核

C.促进红细胞的成熟

D.缩短红细胞产生的时间

E.促进白细胞的分化

Stack is quite simple. Many computer systems have stacks built into their circuitry. They also have machine-level instructions to operate the hardware stack. Stack is（）in computer systems.

A. useless

B. not important

C. simple but important

D. too simple to be useful