Most paragraphs have a "topic sentence" which expresses the central idea. The remaining sentences in the same paragraph expand or support that idea. It has been estimated that between 60-90% of all expository(阐述，说明) paragraphs in English have the topic sentences placed at the beginning of the paragraphs. Always pay special attention to the first sentence of a paragraph; it is most likely In give you the main idea.Sometimes, though, the first sentence in the paragraph does not have the feel of a main idea" sentence. It does not seem to give us enough information to justify a paragraph. The next most likely place to look for the topic sentence is the last sentence of the paragraph. Take this paragraph for example:"Some students prefer a strict teacher who tells them exactly What to do. Others prefer to be left to work on their own. Still others like a democratic type of class. No one teaching method can be devised to satisfy types of class at the same time."Remember that the opening and closing paragraphs of a passage or chapter are particularly important. The opening paragraph suggests the general direction and context of the piece, while the closing paragraph often summarizes the very essence of what has been said. Why do readers should pay special attention to the first sentence of a paragraph That is because a topic sentence is always placed at（）a paragraph.