【内容提示】
兰兰和苗苗是一对孪生姐妹。她们的相貌很像，但穿戴各有所好；她们的气质很相似，爱和她们的年龄同样大小的年轻人在一起玩，讨厌小孩子；爱参加舞会，不爱进图书馆。但是，苗苗喜欢音乐和现代舞，而兰兰一进夜总会就头疼；苗苗喜欢和朋友、老师在一起，而兰兰喜欢独处。她俩多次想住在同一个房间，而且对颜色和家具也有同样的爱好。但是，兰兰喜欢整齐、条理，而苗苗总是乱丢东西；兰兰喜欢早睡早起，苗苗则没有规律，忽而早，忽而晚。
【作文示范】
Twin Sisters
Twins are supposed to be alike， are they not? Well， the twin sisters， Lanlan and Miaomiao do look alike。 Some of the time when they are both dressed up， which is not often， or when they go to the beach， which is not really often either， people recognize the likeness of their features①。 However， they like very different styles of clothes。 Lanlan prefer informal clothes， but Miaomiao dresses like a model， always wearing the latest fashions②。
They have very similar temperaments in most ways。 Lanlan does not get angry easily， enjoys being around people of her own age， finds young children a little irritating③， and would rather spend time at a party than in a library。 In these respects Miaomiao feels the same。 But Miaomiao likes loud music and modern dances， while Lanlan finds that nightclubs④give her a headache。 Miaomiao is always with friends， and is a favorite with all the teachers， whereas Lanlan prefers to be alone at times， and does not really try to impress her teachers。
They have tried to live in the same room several times， and even agreed on the color they liked best and the kind of furniture they wanted。 But Lanlan likes to keep things neat and tidy， while Miaomiao acts as if there were a servant around to pick up all the things that get thrown on the floor or over the edge of the chair or into the bathtub⑤。 Lanlan likes to go to bed early and get up early。 In contrast Miaomiao does not seem to have any definite habits， often goes to bed very late， and then wants to sleep late the next day when Lanlan wants to get the day started。
【词语解释】
①feature ["fi:t>M+]n．（复数）面貌；相貌
②latest fashion["leitist "f$M+n]最新流行式样
③irritating["iriteitiR] a．引起不愉快的
④nightclub["naitl)b] n．夜总会
⑤bathtub["b%:It)b] n． 浴缸；澡盆
【写法指要】
1）本文每个段落都是用异同型（samdiff pattern）组织起来的，先写二者相同点，后写二者的不同点。谈到不同点时，每一段用的都是交替型（seesaw pattern），先说A，后说B，或先说B后说A。
2）用上述方式写对比型说明文时，作者多用表示相反或对照的衔接词（adversatives），如本文中用到的“however， but， while， whereas， in contrast”等，使段落和全文的语义连贯。