假设Px和Py分别表示X和Y商品的价格，当边际替代率MRSxy＞Px/Py，_爱下问搜题

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问题单项选择题

假设P_x和P_y分别表示X和Y商品的价格，当边际替代率MRS_xy＞P_x/P_y，消费者为达到最大效用，他将会（）。

A．增加X商品的购买，减少Y商品的购买

B．减少X商品的购买，增加Y商品的购买

C．同时增加或者减少X和Y商品的购买

D．对X和Y商品的购买数量不发生改变

答案

参考答案：A

解析：

当MRS_xy＞P_x/P_y时，假设MRS_xy=1/0.5，P_x/P_y=1/1，则从不等式的右边来看，消费者减少1单位的商品X的购买，就可以增加1单位的商品Y的购买。从不等式的左边来看，消费者的偏好认为，在减少1单位的商品X时，需要增加0.5单位的商品X，就可以维持原有的满足程度。这样消费者因多得到0.5单位的商品X而使总效应增加。所以在这种情况下，理性的消费者必然会不断减少对Y商品的购买和增加对X商品的购买，以便获得最大效用。

填空题

汽车沿着盘山公路可以驶上高耸入云的云峰，盘山公路修得弯弯曲曲，主要目的是为了，载重货车下山时，其重力势能（填“增大”“减小”或“不变”），为了减小车速，司机师傅不时踩刹车脚踏板，有一部分机械能转化为，途中，汽车要经常停下来，让工作人员用水龙头向车轮闸片部位喷水，这是为了．

完形填空

阅读下面短文，掌握其大意，然后从36-55各题所给的四个选项中，选出最佳选项。
Preparing for tomorrow
Sixth-grade schoolteacher Ms．Shelton believed in readiness．Students remembered how she walked in on the first day of class and began writing words of eighth-grade on the   36   ．They quickly protested that the words were not on their    37    and they couldn’t learn them．
Their teacher insisted that the students could and would learn these    38   ．She said that she would teach them something that should be given．Ms．Shelton    39    by saying that one of the students in the classroom could go on to   40   , maybe even be president someday, and she wanted to prepare them for that day．
Ms．Shelton spoke those words many years ago． 41    did she know that someday one of her students—Jesse Jackson—would take them    42   ．She believed that if they were well prepared, they could   43   high goals．
Ralph Waldo Emerson once said, “People only see what they are    44    to see．” If that’s true, then it is also   45    that they only become what they are prepared to become．And many things in life are just about getting ready．
“I want to be doing something more    46    with my life than what I am doing now,” a young man once said to me．He    47    what he was doing was just not that important．Other people have said things to me such as, “I only   48    I had a meaningful relationship．” And, “I’d really like to get a better job, but I just don’t see   49   ．”
You fill in the blanks．What is it you would like to    50    that isn’t happening? Perhaps the answer is that you are not yet   51   ．Maybe you need more time to prepare before you are truly ready for that which you   52   ．
Think of today as another chance to  53   yourself for the exciting future you are looking for．Today is not wasted．If you desire more from    54   , then you can use today as training．For you will experience only what you are prepared to   55   ．Something wonderful can happen．And you can use today to get ready for tomorrow．

C．pronunciations

B．significant

D．interesting

小题12:A．boasted B．behaved C．felt D looked

A．adventurous

D．intelligent