（1）
why are young people so enthusiastic about computers？it is mainly because they find that
the computer has a large number of desirable properties.first，it's not terribly demanding，and it does what it is told.second，it's easier
to be a friend to a computer，for it won't make fun of you.nor does it scold you or talk back.third，the computer
is more interesting than any other object.like people，it is interactive.when you ask it a question，it gives you an answer.and because it stores great quantities of information，it can oftenanswer more questions，more accurately，than human friends.finally，by programing a computer，a youngster can create a world of
his own.
topic sentence：____________________________________________
______________________________________________________________
developing method：_________________________________________
details：1._______________________________________________
2._______________________________________________
3._______________________________________________
4._______________________________________________
order of organization：________________________________________
（2）
people travel because travel benefits them in a number of ways.first，it enables people to derive much pleasure from seeing sight sand
snapping pictures.second，it provides an effective way to get
their mind off their work.it relieves them from strain and makes them thoroughly relaxed and
ready to resume their work with rennewed efforts.third，it offers an
opportunity to visit old friends and make new friends，too.finally，it allows people to see new customs，learn new things，gain new experience and enables them to come back with broader mind.
topic sentence：____________________________________________
______________________________________________________________
developing method：________________________________________
details：1.______________________________________________
2.______________________________________________
3.______________________________________________
4.______________________________________________
order of organization：______________________________________
exercise 19-1
directions：write a paragraph about the unfavorable effects of advertisements，using order of importance.
________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
exercise 19-2
directions：write a paragraph about the phenomena of the wasting of water，using order of familiarity.
________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
第二十单元 推展段落方法——混合方法
20.1 混合方法（mixed patterns）
到目前为止，我们讨论了九种推展段落方法——1）事实数据法（facts and statistics）；2）叙述法（narration）；3）描述法（description）；4）过程分析法（process analysis）；5）定义法（definition）；6）举例法（examples）；7）比较对比法（comparison
and contrast）；8）分类法（division and classification）；9）因果法（cause and effect）。我们还讨论了四种组织段落的方法：1）时间顺序法（time
order）；2）空间顺序法（space order）；3）重要性顺序法（order of importance）；4）熟悉度顺序法（order
of familiarity）。此外，我们还谈及一个好的段落的三个特征：1）完整性（completeness）；2）统一性（unity）；3）连贯性（coherence）。
我们在前面各单元的示范段落中已经发现，极少段落是仅用一种推展方法的。作者常常在段落中使用一种方法作为支配方法（dominant method），另外一种或数种作为辅助方法（supporting method）。
示范段落20-1
man's knowledge of the past has sometimes been gained in odd ways.one of the oddest incidents
occurred on january 16，1900.an angry
workman broke a crocodile mummy into pieces.he wassurprised to find that the mummy had been wrapped in sheets of
papyrus，the reed
paper of ancient egypt.and on the papyrus there was writing.
20.2示范段落分析
主题句：man's knowledge of the past has
sometimes been gained in odd ways.
组织段落顺序：time order
支配推展方法：example
辅助推展方法：narration
示范段落20-2
there are two kinds of memory：short-term and long-term.information stored in the long-term memory can be recalled at a
later time when it is needed.the information may be kept for days or weeks.in contrast，information stored in the short-term
memory is kept for only a few minutes，usually by repeating the in formation over and over.
20.3示范段落分析
主题句：there are two kinds of memory：short-term and long-term.
组织段落方法：order of familiarity
支配推展方法：division and classification
辅助推展方法：description，contrast
exercise 20-1
directions：write a paragraph on population increase，using cause and effect as the
dominant method，and examples，facts or statistics as the
supporting methods.
why has the world population been increasing so rapidly in the last
decades？_____________________________________________________
______________________________________________________________________________