论述在网络传输中分组与帧的概念，并指出两者的区别。
参考答案：
分组就是把要传输的完整的信息内容按照规定的长度划分为多个数据组后进行传输。帧是网络上所传输的数据最小单元。
分组是一个广义的概念。网络体系结构任一层中的任何一个协议数据单元都可以被称为分组，分组只强调把完整信息划分为小段后传输给接收方，而并未具体要求如何实现这种传输与接收。分组是一个与硬件无关的逻辑概念。
帧也是一个分组，是指分组在一个具体网络上的实现，帧只能用于表示网络体系结构中第二层协议所定义的分组。
请认真阅读下列短文, 并根据所读内容在文章后表格中的空格里填入一个最恰当的单词。注意：每个空格只填一个单词。 The word science is heard so often in modern times that almost everybody has an idea of its meaning. However, its definition is difficult for many people. The meaning of the term is confusing, but everyone should understand its meaning and objectives (目标). Just to make the explanation as simple as possible, suppose science is defined as classified knowledge or facts. Even in the true science, distinguishing fact from fiction is not always easy. For this reason great care should be taken to distinguish between beliefs and truths. There is no danger as long as a clear difference is made between temporary and proved explanations. For example, hypotheses(假设) and theories are attempts to explain natural phenomena. From these positions the scientist continues to experiment and observe until they are proved or discredited. The exact status of any explanation should be clearly labeled to avoid confusion. The objectives of science are primarily the discovery and later the understanding of the unknown. Man cannot be satisfied with recognizing that secrets exist in nature of that questions are unanswerable; he must solve them. Toward that end, specialists in the field of biology and related fields of interest are directing much of their time and energy. Actually, two basic approaches lead to the discovery of new information. One, aimed at satisfying curiosity, is referred to as pure science. Sometimes practical-minded people miss the point of pure science in thinking only of its immediate application for economic rewards. However, one should remember that the construction of the microscope had to come before the discovery of the cell. The host of scientists devoting their lives to pure science are not apologetic about ignoring the practical side of their discoveries; they know from experience that most knowledge is eventually applied. The other is aimed at using knowledge for specific purposes--for instance, improving health, raising standards of living, or creating new consumer products. In this case, knowledge is put to economic use. Such an approach is referred to as applied science.
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