People used to tell the time of day by shadows. They used sundials to do so. In some sundials it was the length of a shadow which told the time of day. In some sundials it was the position of the shadow. Some sundials are still in use.
The main idea of the passage is__________.
A. Sundials look nice in gardens.
B. By using sundials, people used to tell the time of day by the length of shadows.
C. In the past sundials were used to tell time.
D. Sundials, which tell the time of the day by the length or position of shadows, were once used to tell time.
(1)People used to tell the time of day by shadows.(2)They used sundials to do so.(3)In some sundials it was the length of a shadow which told the time of day.(4)In some sundials it was the position of the shadow. (5) Some sundials are still in use.
阅读文章中往往会有一些承上启下的连接词，表明上下文、前后句的联系。利用这些词有助于进行层次分析，如first，second，third，finally，to begin with，and，more，even more，moreover，more than that，besides，furthermore，also，likewise，again，next，then，in addition to，some，others，still others，above all，another，equally，lastly。这些词或词组表示并列关系，他们所属的句子必然属于同一层，而且往往是处于主题句下面的第二层。
2.利用重复的词或词组
重复的词或词组往往表示一些并列的分论点或论据，以示强调。如:(1)Futurologists predict that life will probably be very different in 2050. (2) TV channels will have disappeared. (3) Robots will have replaced people in factories. (4) Medical technology will have conquered many diseases. 以上这些重复的will有排比的意味，表示它们都处于同一层，很好地支持了主题句（1）。
(1)It is found that a child plays games for very important reasons. (2)He can find himself being a useful partner to someone of whom he is ordinarily afraid. (3)He becomes a leader when it comes to his turn.
