听力原文： Man: My secretary tells me that you'd like to know something about mechanical engineering. What I can do is give you some idea of the variety of specialties within the field. Woman: I'd appreciate that very much. Man: One of the oldest mechanical engineering areas is machine design. First, we need to know the purpose, of a particular machine, whether it's a crane or a tool or a steam engine. Then, if we know the loads that this machine will carry, we can make the most efficient use of the materials we have. Woman: I see. Is heating included in this field? Man: Oh, yes. Heating, refrigeration, and air conditioning rely quite a lot on thermodynamics and theories of heat transfer. The goal is to make the most efficient use of power. This area can be quite involved with mathematics. Woman: I've heard of the Carnot cycle. Does this concern the mechanical engineer? Man: Very much so. The whole field of internal combustion engines is based on the principles set out by Carnot. The mechanical engineer deals with two and four-cycle engines, gasoline and diesel engines, gas turbines, and the like. Woman: Isn't that part of automotive engineering? Man: Yes. This is one of our largest industries. Woman: What about the aircraft industry? Man: Of course. Aeronautical engineering became a very large field with the widespread use of airplanes. Now, with space travel, it promises to grow even larger. Woman: Well, you've been most helpful, sir. Man: Not at all. Come in again. 27.Why has the woman come to the man's place? 28.What is the man's field of research? 29.Which of the following subjects is involved in mechanical engineering? 30.Who was Carnet according to the man? (47)