二维离散型随机变量(X，Y)的联合分布如下图，

那么，x与Y之间的关系是(65)。
A．相关但不独立
B．独立但不相关
C．相关且独立
D．既不独立也不相关

未分类题In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet. How does the developer of a large database system achieve(71)and data independence? How does the developer make certain that stored items are(72)and do not simply disappear in the immensities of the database, as if in quicksand? One solution is to set up a(73)system, in which all data (the internal level), all records and files (the conceptual level), and all user interfaces (the external level) are controlled by one central programming group. This may seem the most useful solution. But worldwide enterprises such as the meteorological and satellite tracking networks, IBM, and General Motors gather and record information at a very large number of locations. To stay flexible and avoid top - heaviness, such an organization might want to avoid excessive centralization. A centralized system is(74), but it may not be responsive to user needs. This is particularly true in a large organization - the worldwide meteorological network, for example, Data-gathering methods in the Himalayas, the equatorial jungles are different in very possible way. It is reasonable to believe that the best choices for the corresponding data storage and access structures ought to be just as different. A centralized database system would not(75)such differences.A．consistencyB．identificationC．coherenceD．convergence

单项选择题如果消费者消费的商品X和商品Y的价格之比为1.25，它们的边际效用之比为2，那么消费应该( )。 A．增加对X的购买和减少对Y的购买 B．增加对Y的购买和减少对X的购买 C．同时增加对X和Y的购买 D．同时减少对X和Y的购买

单项选择题已知某正常商品的价格下降时，替代效应为+2，则收入效应可能为( )。 A．-4 B．-2 C．-1 D．+1

未分类题某外国甲公司欲与中国乙公司共同兴办中外合资经营企业,双方合作企业设在北京。下列不属于中国合作者向审批机关申请设立中外合作企业时应提交的文件包括( )。

单项选择题当两种商品X和Y的效用函数为U(X，Y)＝XY时，下列效用函数中描述了相同的偏好次序的是( )。 A．U＝(X-5)(Y-5) B．U＝(X 5)(Y 5) C．U＝(X+5)(Y+5) D．B和C都正确