The word science is heard so often in mode

问题：

The word science is heard so often in modem times that almost everybody has some notion of its meaning. On the other hand, its definition is difficult for many people. The meaning of the term is confused, but everyone should understand its meaning and objectives. Just to make the explanation as simple as possible, suppose science is defined as classified knowledge (facts).
Even in the true sciences 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 and theories are attempts to explain natural phenomena. From these positions the scientist continues to experiment and observe until they are proved or discredited (使不相信). The exact status of any explanation should be clearly labeled to avoid confusion.
The objectives of science are primarily the discovery and the subsequent understanding of the unknown. Man cannot be satisfied with recognizing that secrets exist in nature or 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. 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.
Sometimes practical-minded people miss the point of pure science in thinking only of its immediate application for economic rewards. Chemists responsible for many of the discoveries could hardly have anticipated that their findings would one day result in applications of such a practical nature as those directly related to life and death. The discovery of one bit of information opens the door to the discovery of another. Some discoveries seem so simple that one is amazed they were not made years ago; however, one should remember that the construction of the microscope had to precede the discovery of the cell. The host of scientists dedicating 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.

To define science we may simply call it ______.

A．classified knowledge

B．the study of unrelated fields

C．the study of unrelated subjects

D．an attempt to explain natural phenomena