以下有关急性放射病的描述哪项是错误的

A．是一种全身性疾病
B．可以分为I度和Ⅱ度
C．根据临床特点和基本病理改变可分为骨髓型、胃肠型、脑型
D．是人体一次或短时间内分次受到大剂量照射引起的
E．是国家法定职业病

(74) systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and (75) on the disk, and controlling peripheral devices such as disk drives and printers.

A．contents

B．diectories

C．directions

D．direct