如我们要论证一个这样的主题句，可以用因果法来描述：Older people could make their own effort to help young people in daily life events. It is undeniable that the life experience elderly people owned are much more valuable and richer by learning from which, the younger generation could learn many lessons and avoid making same mistakes. Also, senior citizens do have more free time after retirement. Therefore, they can help do a great number of household chores, which could relieve the burden on their adult children, many of whom have both their careers to develop and their own families top provide for.
Professors benefit from appearing on television due to doing so they acquire reputations as authorities in their academic fields among much wider audience than they have on campus. If a professor published views in an academic journal, only other scholars can learn about and appreciate those views. But when a professor appears on TV, thousands of people outside, the narrow academic community become aware of the professor’s ideas. So when professors share their ideas with the television audience, the professors’ importance as scholars is enhanced.（使用了3个假设方法把主题句说明的很清楚）
International Fast foods tend to be less healthy than home-cooked meal. Fast food is a kind of processed food which contains high level of salt, fat, sugar, cholesterol and is well known for its heavy reliance on meat. Such food always refers to junk food like hamburger, pizza, kebab ,fish and chips and some instant foods ,most of which are fried and toasted, and thereby not only lacking basic nutrients, but also containing large amounts of toxic substance. Therefore, it is the culprit of several diseases such as heart disease, obesity, diabetes and cancer.（把international fast food解释清楚了就能把主题句论证清楚了。）
The first reason is that many people consider the environmental problem as a future concern. Environmental reports often warn us of the dire consequence of climate change or energy crises 100 or 200 years later. As a result, many people feel that money and time is better spending on solving more immediate problems such as housing shortage and traffic congestion that on preventing a disaster that only predicted to happen in the future.
Anything which encourages language learning benefits society culturally and economically and early exposure to language learning contributes to this. Young children’s innate abilities should be harnessed to make these benefits more achievable.
Traditionally, children have begun studying foreign languages at secondary school, but introducing them earlier is recommended by some educationalists.（分词结构做状语）
This policy has been adopted by some educational authorities or individual schools, with both positive and negative outcomes.（伴随状态）
The obvious argument in its favor is that young children pick up languages much more easily than teenagers.（表语从句）
Their brains are still programmed to acquire their mother tongue, which facilitates learning another language, and unlike adolescents, they are not inhibited by self-consciousness.（非限定性定语从句+平行结构，严格来说这是个并列复合句，比较复杂）
The greater flexibility of the primary timetable allows for more frequence, shorter sessions and for a play-centered approach, thus maintaining learners’ enthusiasm and progress.（大量平行结构的出先，既拉长了句子，又丰富了词汇，何乐而不为呢？）
If primary language teaching is not standardized, secondary schools could be faced with a great variety of levels in different languages within their intakes, resulting in a classroom experienced which undoes the earlier gains.（条件状语从句+结果状语后置）
例句：It would facilitate matters if they were more co-operative.
例句：Modern inventions facilitate housework.
例句：No matter what level of exposure you have, your lung