72．How does the writer support the underlined statement in Paragraph2?
(A)By giving instructions．
(B)By analyzing cause and effect．
(C)By following the order of time．
(D)By giving examples．

文章段落结构。第二段是总分结构，主旨句在段首段尾。本句后面就是对于这个观点的具体解释，用火车轮船飞机的例子来说明论点。