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问题 单项选择题

下列关于时间片轮转法的叙述中，哪一个是不正确的？

A．在时间片轮转法中，系统将CPU时间划分成一个个时间段

B．就绪队列中的各进程轮流在CPU上运行，每次运行一个时间片

C．当时间片结束时，运行进程自动让出CPU，该进程进入等待队列

D．如果时间片长度很小，则调度程序剥夺CPU的次数频繁，加重系统开销

答案

参考答案：C

解析：在时间片轮转法中，当时间片结束时，就强迫运行进程让出CPU，该进程进入就绪队列，等待 下一次调度。时间片的选取很重要，将直接影响系统开销和响应时间。如果时间片很小，可 能会加重系统开销；反之，如果时间片过长，则轮转法就变成先进先出算法。

单项选择题

微型计算机存储系统中，PROM是

A．可读写存储器

B．动态随机存取存储器

C．只读存储器-

D．可编程只读存储器
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单项选择题

I will never forget the year I was about twelve years old. My mother told us that we would not be (16) Christmas gifts because there was not enough money. I felt sad and thought, "What would I say when the other kids asked what I’ d (17) " Just when I started to (18) that there would not be a Christmas that year, three women (19) at our house with gifts for all of us. For me they brought a doll. I felt such a sense of (20) that I would no longer have to be embarrassed when I returned to school. I wasn’t (21) . Somebody had thought (22) of me to bring me a gift.

Years later, when I stood in the kitchen of my new house, thinking how I wanted to make my (23) Christmas there special and memorable, I (24) remembered the women’s visit. I decided that I wanted to create that same feeling of (25) for as many children as I could possibly reach.

So I (26) a plan and gathered forty people from my company to help. We gathered about 125 orphans (孤儿) at the Christmas party. For every child, we wrapped colorful packages filled with

toys, clothes, and school supplies, (27) with a child’ s name. We wanted all of them to know they were (28) Before I called out their names and handed them their gifts, I (29) them that they couldn’t open their presents (30) every child had come forward. Finally the (31) they had been waiting for came as I called out, "One, two, three. Open your presents!" As the children opened their packages, their faces beamed and their bright smiles (32) up the room. The (33) in the room was obvious, and (34) wasn’ t just about toys. It was a feeling, and the feeling I knew (35) that Christmas so long ago when the women came to visit. I wasn’t forgotten. Somebody thought of me. I matter.

35（）

A.by 

B.till 

C.for 

D.from
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