Section B
Directions: There are 2 passages in this section．Each passage is followed by some questions or unfinished statements．For each of them there are four choices marked A, B, C and D．You should decide on the best choice.
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(合金) 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 wheel in a turbo-jet must withstand temperatures as high as 1,600 degrees Fahrenheit, so aircraft designers had to turn to the research metallurgist(冶金学者) for the development of metals and alloys that would do the job in jet-propelled 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 division．And, with finer and finer divisions, 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.
The statement 'the horizons of science have expanded'(Line 1, Para．1) means that______.