Another American, Henry Ford, developed the idea of assembly line. Before Ford introduced the assembly line, each car was built by hand. Such a process was, of course, very slow. As a result, automobiles were so expensive that only rich people could afford them. Ford proposed a system in which each worker would have a special job to do. One person, for example, would make only a portion of the wheels. Another would insert the bolts that held the wheels to the car. Each worker needed to learn only one or two routine tasks.
　　（3）主题句在段中。
　　有时段落是先介绍背景和细节，接着用一句综合或概括性的话概括前面所说的内容或事例，然后再围绕主题展开对有关问题的深入讨论。这种文章的主题句往往会在段落中间出现，但不是就在正中间。
　　例如：
　　In spite of the fact that cars from Germany and Japan are flooding the American market, Ford, General Motors, and Chrysler are employing more workers than ever before. The flood of cheaper foreign cars has not cost American autoworkers their jobs as some experts predicted. Ford operates as far as Asia, and General Motors is considered Australia's biggest employer. Yet General Motors has its huge American work force and employs hundreds of people every day to meet the needs of an insatiable society.
　　What is the main idea of the passage?
　　A. The foreign cars have not taken away the jobs of American autoworkers.
　　B. General Motors is one of the largest car producers.
　　C. Ford operates not only in the USA, but also in Asia.
　　D. The flood of cheaper foreign cars is terrible for American autoworkers.
　　上面这段话的主题句位于本段的中间：The flood of cheaper foreign cars has not cost American autoworkers their jobs as some experts expected. 据此，此题的正确答案应为 A.
　　请阅读下列短文并找出主题句
　　No. 1
　　Despite the fact that cars from Germany and Japan are flooding the American Market. Ford, General Motors and Chrysler are hiring more workers than ever before. The flood of cheaper foreign cars has not cost American autoworkers their jobs as some experts predicted. Ford operates as far as Asia, and General Motors is considered Australia's biggest employer. Yet GM has its huge American work force and hires hundreds of people every day to meet the needs of an insatiable society.
　　No.2
　　What does the doctor need to know about his patient? In the initial interview the doctor needs to know as much as possible about him, as it relates to his ailments. This is the medical history, and although informal and brief, it is the first step at arriving at a diagnosis. The sooner a correct diagnosis, the quicker he can get effective therapy
　　No.3
　　Just as I settle down to read or watch television, he demands that I play with him. If I get a telephone call, he screams in the background or knocks something over. I always have to hang up to find out what's wrong with him. Baby-sitting with my little brother is no fun. He refuses. to let me eat a snack in peace. Usually he wants half of whatever I have to eat. Then, when he finally grows tired, it takes about an hour for him to fall asleep.
　　Baby-sitting with my little brother is no fun
　　上面三篇文章的主题句分别为：
　　No.1 The flood of cheaper foreign cars has not cost American autoworkers their jobs as some experts predicted.
　　No2 In the initial interview the doctor needs to know as much as possible about him, as it relates to his ailments.
　　No3 Baby-sitting with my little brother is no fun.

　　（二）找主题词
　　有时段落中没有明显的主题句。作者用一种间接的方式表达了段落的中心思想。这时我们不能轻而易举地判断出主旨或主题这样，主题句是含蓄的，它隐含在短文或段落之中，需要考生从段落中寻找主题词或词组。然后用这些主题词或词组概括和归纳出段落的中心思想。
　　Bats are the only animals that truly fly. These animals use their leathery wings differently from birds. Birds flap their wings up and down, while bats use both their wings and legs, which makes them seem as if they are swimming through the air. Even though bats take much longer, stronger strokes than birds, they still can beat their wings as often as twenty times per second!
　　此段落的主题词是 bats, birds , different , fly
　　归纳出段落的中心思想是：Bats are different from birds in flying.
　　Some people like to go to beach or a lake for recreation. They enjoy the swimming or boating that is available there. Other people, especially in the hot summer, prefer clean air and cool mountain breezes. Some people like excitement and entertainment. They got to shows and nightclubs. Still other people find that staying home with the family and enjoying the togetherness of spending time with loved ones is the most pleasurable experience of all.