留预教材对句式多样性和句子简洁性的启示：从句的省略
在平时的写作教学中，老师发现很多学生对于状语从句或定语从句掌握得不错，并且可以在作文中熟练使用。但其实如果在一篇作文中总是出现某类从句，句型没有太大的变化，这样在句式多样性上会比较缺乏。咱们新航道留学预备读写教材可谓是写作素材的宝库，老师也从中受到了一些启发。老师会结合留预四级教材给大家介绍状语从句和定语从句的省略方法，帮助大家实现句式的多样性和句子的简洁性。
（一）状语从句的省略
状语从句的省略有两个前提条件，大家可以通过观察下面的例句，进行归纳。
例句1：But when placed in a container with an open end, the powder created bright flames, sparks, and thick smoke. 【但是当（粉末）被放在一个一端开口的容器里时，粉末会产生明亮的火焰、火花和浓烟。】
例句1包含一个when引导的状语从句，但是这个从句其实是不完整的。我们可以把从句补充完整：But when （the power was）placed in a container with an open end。所以我们可以总结出，省略状语从句需要两个条件：①主句和从句主语一致；②从句中包含be动词。
下面大家可以尝试改写下面的句子，答案会在文末给出。
练习1：As he was lying in the grass, he thought of the seaside where he had spent the summer.
练习2：She stood at the door as if she was waiting for someone.
练习3：Although she was somewhat thinner than desirable, She is in good health.
（二）定语从句的省略
定语从句的省略其实相当于现在分词或过去分词作后置定语。分词作后置定语的意思是分词短语作为定语放在修饰的名词或代词的后面。大家可以结合例句来理解。
例句2：Researchers have studied language used by sports fans to talk about their teams. 【研究人员研究了被体育迷们用来谈论他们球队的语言。】
例句中的“language”由它后面的“used by sports fans to talk about their team”过去分词短语修饰，相当于省略的定语从句language which/that is used by sports fans to talk about their teams。而且“language”和“used”是被动关系，表达“被...使用的语言”。
例句3：The shopping center standing across the street was built last year. 【街对面的那家购物中心是去年建的。】
例句中“shopping center”由“standing across the street”现在分词短语修饰，相当于定语从句the shopping center which stands across the street。其中“shopping center”和“standing across the street”是主动关系，表达“在街上的购物中心”。大家尤其要注意现在分词作后置定语的前提条件：现在分词短语所表示的动作，在时间上同主句谓语动词的时间相一致，或表示经常性，长久性情况。例句中，购物中心建在街上，是一个长久性的情况，所以可以使用现在分词作后置定语。
大家还是可以通过练习下面的句子改写，来理解这个方法。
练习4：These trucks carry goods which are exported to foreign countries.
练习5：Those were the problems which puzzled her day and night.
练习6：He was a teacher who was respected by all his students.
以上就是状语从句和定语从句的省略方法，大家可以结合例句理解，然后进行练习。在掌握了从句的使用方法，能够正确地写出状语和定语从句之后，同学们可以尝试从句的省略，避免作文中全部的状语和定语都是从句的形式，也可以使用这种分词作状语和定语的方法。实现句式的多样性和句子的简洁性。
练习答案
练习1：As lying in the grass, he thought of the seaside where he had spent the summer.
练习2：She stood at the door as if waiting for someone.
练习3：Although she was somewhat thinner than desirable, She is in good health.
练习4：These trucks carry goods exported to foreign countries.
练习5：Those were the problems puzzling her day and night.
练习6：He was a teacher respected by all his students.
参考资料：留学预备读写4级教材，大学英语语法
