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问题 填空题

已知△ABC∽△DEF，AB=6cm，DE="12cm," 且△ABC的周长为24cm，则△DEF的周长为          。

答案

48 cm

题目分析：已知△ABC∽△DEF，所以，因为AB=6cm，DE=12cm,所以=，又因为△ABC的周长为24cm，即AB+BC+CA=24；则△DEF的周长=DE+EF+DF=2（AB+BC+CA）=48

点评：本题考查相似三角形，解答本题的关键是掌握相似三角形的性质，运用其性质来解决本题

单项选择题

使用单位在采用新工艺、新技术、新设备、新材料时，应当对（）进行相应的安全生产教育培训。

A、负责人

B、技术人员

C、作业人员

D、安全管理人员
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单项选择题

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
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