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1. 双名词从句式
Another reason why people from the countryside transfer to the cityis because of the modern conveniencesthat city living brings.
解析：适用于引入原因(带题目关键词)
句型框架：主语从句+ is because of the 原因 +宾语从句(包括主从，宾从两个名词性从句)
例句中，people from the countryside transfer to the city 是对题目关键信息的复述，句型中“原因”部分使用一个名词或名词词组。
Exercise:causes of congestion in megacities
2. 三组P+O式
Today more and more people rely on cars instead of walking, have less physical demands at workand prefer inactive leisure activities. This results inburning less caloriesand gaining weight.
解析：适用于解释句，说明三种具体原因或结论段总结原因和结果
句型框架：主语+P.O.1 , P.O.2 and P.O.3 . This results in doing sth.1and doing sth.2.
例句中，三组P+O (谓语+宾语)是平行结构，第二句的”This” 指代三组P+O; doing sth.1 是result，doing sth.2是ultimate result。
Exercise:causes of overpopulation
3. “原因+细化方面解释” 式
Effluentsare another by-product of industries which poses threat to the environment;leather and tanning industries, petroleum industriesand chemical manufacturing industriescreate major waste productswhich are released directly into nearby streams without treatment, creating river pollution and causing harm to aquatic life.
解析：适用于说明一个原因(论点)后紧接着把这个原因的几个方面具体化论述。
句型框架：原因is another by-product of … which poses threat to 主题词; 具体方面1，具体方面2and 具体方面3create… which are V+ed ….without…, V+ing …..to …
例句中，which are…的部分是定语从句，Ving…to…是非谓语用法。
Exercise:cyber crime
4. X(root cause), Y(cause), Z(result)式
Some people believe that global warmingis a result of burning fossil fuels, as this causesincreased carbon dioxidein the atmosphere.
解析: 这里我们把造成global warming (result)的原因分为burning fossil fuels(root cause)和increased carbon dioxide(cause), 原因和根本原因，然后用适合的句式组织起来，使得逻辑论证层次更丰富。
句型框架： Some people believe that …(result) is a result of … (root cause), as this causes ….(cause).
具体的句式组织还可以是以下五种，R(result), C(cause), RC (root cause):
(R) has been directly affected by (RC), as this allows for (C).
As a result of (RC) leading to (C), (R) has been possible.
(RC), thus allowing for (C), has resulted in (R).
(RC) results in (C), which in turn leads to (R).
Given (RC), it follows that (C) would mean (R)
5. “双非谓语” 结构
Air pollution resulting from the factory and vehicle emission poses serious health concerns, considering the irritation of the eyes, nose, and throat, as well as increased risk of heart attack.
解析：把问题的原因和具体结果都用非谓语形式体现，主语只说关键词造成问题(概括性的名词)，即air pollutionposes serious health concerns.
句型框架：关键词 resulting from… and … poses serious …concerns, considering … as well as…
例句中，描述air pollution 的形成原因部分resulting from和造成的健康问题具体包括什么considering都使用的是非谓语形式。
Exercise: cause and effect of social networking
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