题目内容

设S=Q×Q，其中Q为有理数集合，定义S上的二元运算 * ，
＜a，b＞，＜x，y＞∈S有＜a，b＞ * ＜x，y＞=＜ax，ay+b＞则下面说法中，正确的是
Ⅰ．S上的二元运算 * 是可交换的
Ⅱ.S上的二元运算 * 是可结合的
Ⅲ．* 运算存在单位元
Ⅳ．* 存在零元

A. Ⅰ和Ⅱ
B. Ⅰ、Ⅱ和Ⅲ
C. Ⅲ和Ⅳ
D. Ⅱ和Ⅲ

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A．In the front of the school gate.B．In the front of the school.C．In front of the school

A. In the front of the school gate.
B. In the front of the school.
C. In front of the school gate.
D. In front of the school.

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听力原文：W: My mother told me to keep away from the swimming pool
M: Did she？ Then shall we go to the park to roller-skate？
W: Good idea! I am crazy about roller-skates! When shall we go？
M: What time suits you？ It doesn't make any difference to me.
W: Shall we meet in front of the school gate at 8:00 a.m. and go to the park together？
M: No problem. By the way, you have to wear a helmet when roller-skating. Do you have one？
W: Oh, dear, I don't.
M: Don't worry. I have two helmets. I can lend you one tomorrow.
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A. Because she dislikes swimming.
Because her mother forbids her to swim.
C. Because she has to go to roller-skate.
D. Because she is crazy about roller-skates.

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某计算机有9条指令，其使用频度如表所示
则其哈夫曼码长为

A. 2．2
B. 2．41
C. 2．42
D. 2．43

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粒细胞缺乏症可出现的临床表现是()E．

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A. Ⅰ和Ⅱ B. Ⅰ、Ⅱ和Ⅲ C. Ⅲ和Ⅳ D. Ⅱ和Ⅲ

A．In the front of the school gate.B．In the front of the school.C．In front of the school

某计算机有9条指令，其使用频度如表所示则其哈夫曼码长为

粒细胞缺乏症可出现的临床表现是()E．

A. Ⅰ和Ⅱ
B. Ⅰ、Ⅱ和Ⅲ
C. Ⅲ和Ⅳ
D. Ⅱ和Ⅲ

某计算机有9条指令，其使用频度如表所示
则其哈夫曼码长为