2.主题句的位置 主题句的位置可以在段首： london′s weather is very strange .it can rain several times a day.each time the rain may come suddenly after the sun is shining brightly.the air is damp(潮湿的)and chill(冷的)right through july.on one march afternoon on hampton heath last year it rained three times,there was one hail(冰雹)storm,and the sun shone brilliantly-all this within two hours′s time.it is not unusual to see men and women rushing down the street on a sunny morning with umbrellas on their arms.no one knows what the next few moments will bring. 主题句的位置可以在段落中间： 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(快餐)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. 主题句的位置可以在段尾： doctors are of the opinion that most people cannot live beyond 100 years,but a growing number of scientists believe that the aging process can be controlled.there are more than 12 000 americans over 100 years old,and their numbers are increasing each year.dr？james langley of chicago claims that,theoretically and under ideal(理想的)conditions,animals,including man,can live six times longer than their normal period of growth.a person′s period of growth lasts about 25 years.if dr.langley′s theory is accurate(准确的), future generations can expect a life span(寿命)of 150 years . 主题句的位置可在段首段尾同时出现： good manners are important in all countries,but ways of expressing good manners are different from country to country .americans eat with knives and forks(叉)；japanese eat with chopsticks(筷子).americans say"hi"when they meet.japanese bow.many american men open doors for women.japanese men do not.on the surface,it appears that good manners in america are not good manners in japan,and in a way this is true.but in any country,the only manners that are important are those involving one person′s behavior toward another person.in all countries it is good manners to behave considerately toward others and bad manners not to. it is only the way of behaving politely that differs from country to country.