主题句作文
主题句作文是CET-4写作中常见的一种作文形式。这是一种控制性作文，旨在控制考生的写作范围，要求考生按所给每个段落的第一句续写，完成各段落，但同时它也为考生提供了段落扩展的有利条件，有利于考生在文章的结构和内容安排上不出偏差。因此，主题句作文审题的主要任务之一是审段首句。审题时抓住各段首句的关键词语，仔细斟酌每个段首句的内涵和外延，并把段首句同文章的标题联系起来分析，找出标题与各段首句之间的关系，以确定段落的扩展方式和材料的筛选。在具体写作时要以段首句为线索，合理安排有关材料或细节，将段落充分展开，并保证各段落在意义上连成一体，形式上互为统一，语气上一气呵成，否则就会偏离主题。下面以1989年6月的作文“What Would Happen If There Were No Power?”为例：
               What Would Happen If There Were No Power
1. Ever since early this century, electricity has become an essential part of our modern life.
2. If there were no electric power,             
3. Therefore
第一个段首句所包含的信息是：电在现代生活中的作用。句中的关键词是an essential part of our modern life， 即该段的中心思想。因此，可通过举例、说明、分析等手法扩展完成该段落，阐明电在现代生活中的作用。
Ever since early this century, electricity has become an essential part of our modern life. It is much used in both our life and production. We use electricity to light our houses, carry our messages through space, work computers, show us the inside of our bodies, and drive all kinds of machines, such as washing machines, air conditioners, pumping stations and various machines on the production line.
第二段“If there were no electric power”这是一个主从复合句，虽然只给出了从句部分，但它表明该段与第一段是转折关系。因此，第二段应写成与第一段意思相反，形成对照的一个段落，说明“如果没有电”，现代生活将会是什么样。
If there were no electric power, the modern world would be in great trouble. Many of our industries would stop production because the motors that power the machines would fail. The transportation systems would fall apart without a supply of electricity. Electric trains would all stop, and motor vehicles could not be operated. For the same reason, aeroplanes could not fly. Probably the worst effect would be felt on the communications systems. The telephone, radio, television and radar would be put out of action.
第三段只给出一个单词“Therefore”，但这是一个信号词，表明该段是全文的结论部分。因此，该段落应总结前两段的内容，强调现代生活离不开电这一主题，并点明：必须节约用电和开辟新的能源。
Therefore there are two points we must pay attention to. First, we should save electricity and energy resources such as coal and oil with all our efforts because most of the electricity we use is produced by machine with coal or oil as fuel. On the other hand, people should also explore other sources of power, for instance, water, sea tide, wind power, and harness solar energy and energy from within the earth, and so on. Scientists have to discover a substance that will replace electricity.

提纲作文
如：1998年6月的作文“Numbers and Luck”