As the horizons of science have expanded, two main groups of scientists have emerged. One is the pure scientist; the other, the applied scientist.

The pure or theoretical scientist does original research in order to understand the basic laws of nature that govern our world. The applied scientist adapts this knowledge to practical problems. Neither is more important than the other, however, for the two groups are very much related.

Sometimes the applied scientist finds the “problems” for the theoretical scientist to work on. Let’s take a particular problem of the aircraft industry: heat-resistant metals. Many of the metals and alloys that perform satisfactorily in a car cannot be used in a jet-propelled plane. New alloys must be used, because the jet engine operates at a much higher temperature than an automobile engine. The turbine（涡轮）wheel in a turbo-jet（涡 轮喷气机）must withstand temperatures as high as 1600 degrees Fahrenheit, so aircraft designers had to turn to the metallurgist（冶金家） for the development of metals and alloys that would do the job in jetpropelled planes.

Dividing scientists into two groups—pure and applied—is only one broad way of classifying them, however. When scientific knowledge was very limited, there was no need for men to specialize. Today, with the great body of scientific knowledge, scientists specialize in many different fields. Within each field, there is even further subdivision. And, with finer and finer subdivisions, the various sciences have become more and more interrelated until no one branch is entirely independent of the others. Many new specialties—geophysics and biochemistry, for example—have resulted from combining the knowledge of two or more sciences.

Statement “the horizons of science have expanded” (Line 1, Para. 1) means that ________.

The applied scientist ________.

The example given in the third paragraph illustrates how ________.

Finer and finer subdivision in the field of science has led to ________.

We can learn from the passage that ________.