无锡惠山泉因著名的二胡名曲（）而为世人所知。

在上述给定的速率要求下，该飞机需要模拟何种运动，方可在一定范围内任意选择失重时间的长短？试定量讨论影响失重时间长短的因素

关于月经周期中，生殖激素的变化不正确的是（）

A.经前2天，血E、P水平下降

B.经期2天，FSH升高、LH脉冲分泌频率增快

C.在LH峰出现后，血P浓度下降

D.排卵后，E、P升高

E.孕激素抑制GnRH分泌频率

我国最大的工业城市和商业中心[ ]

A．重庆

B．上海

C．北京

D．天津

我国各地形中，面积最广阔的是              （   ）

A．平原

B．高原

C．山地

D．丘陵

In looking at the class structure of an entire system, we may find that its inheritance (1) is either wide and shallow, narrow and deep, or balanced. Class structures that are wide and shallow usually represent forests of (2) classes that can be mixed and matched. Class structures that are narrow and deep represent trees of classes that are related by a common ancestor. There are advantages and disadvantages to each approach. Forests of classes are more loosely (3) , but they may not exploit all the commonality that exists. Trees of classes exploit this commonality, so that individual classes are smaller than in forests. However, to understand a particular class, it is usually necessary to understand the meaning of all the classes it inherits from or uses. The proper shape of a class structure is highly problem-dependent.
We must make similar trade-offs among inheritance, aggregation, and using relation- ships. For example, should the class Car inherit, contain, or use the classes named Engine and Wheel In this case, we suggest that an (4) relationship is more appropriate than inheritance relationship. Meyer states that between the class A and B," (5) is appropriate if every instance of B may also be viewed as an instance of A. The client relationship is appropriate when every instance of B simply possesses one or more attributes of A". From another perspective, if the behavior of an object is more than the sum of its individual parts, then creating an aggregation relationship rather than an inheritance relationship between the appropriate classes is probably superior.

(5)

A．aggregation

B．inheritance

C．association

D．using