As the horizons of science have expanded, two main groups of scientists have (26) . One is the pure scientist; the other, the applied scientist. Dividing scientists into two groups pure and applied is only one broad way of (27) them. The pure or theoretical scientist does (28) in order to understand the basic laws of nature that (29) our world. The applied scientist (30) practical problems. Neither is more important than the other, however, for the two groups are very much related.
Sometimes, however, the applied scientist finds the "problems" for the theoretical scientist to (31) . Let’s take a particular problem of the aircraft industry: (32) metals. Many of the metals and alloys which perform (33) in a car cannot be used in a jet-propelled plane. New alloys must be used, because the jet engine (34) a much higher temperatures than automobile engine. The turbine wheel in a turbojet must (35) as high as 1,600 degrees Fahrenheit, so aircraft designers had to turn to the research metallurgist (冶金学家) for the development of metals and alloys that would do the job in jet-propelled planes.