平均访问时间体现硬盘读/写速度，它包括硬盘寻道时间和等待时间，即平均访问时间＝平均寻道时间+平均等待时间。
参考答案：对
— My teacher says she's cancelling the class play. I just can't understand.
— ______.You were looking forward to it. [ ]
A. It doesn't matter
B. It's very unwise of her
C. Don't worry about it
D. You must be disappointed
阿片类物质的药理作用不包括（）
A.镇痛
B.抑制咳嗽中枢
C.瞳孔扩大
D.抑制呼吸
E.导致欣快
