中心思想的作用是导向(control)和制约(limit)。所谓导向就是规定段落的发展脉络，所谓制约就是限制主题的覆盖范围，两者不可分割。没有导向，内容就会离题或偏题;没有制约，内容就可能超出一个段落所能容纳的范围。
大学生英语演讲稿范文一：
Welcome to Guangdong
Ladies and Gentlemen, Honorable Judges, Good afternoon.
I come from one of the most lovely and attractive areas of China, the Pearl River Delta of Guangdong Province and I'd love to say a few words about this area that is so dear to my heart.
Guangdong Province is a magically beautiful wonderland, with endless natural treasures. The lush and green mountains are inhabited by songbirds and exotic animals; the farm land is fertile and productive, providing all of its people with wonderfully nutritious grains and all the fruits they need to be healthy and strong. The Pearl River meanders through the province and eventually comes to our beautiful seashore with crystal clear blue water, flourishing with all kinds of different fish and sea creatures. All these natural advantages help to boost the ever-expanding economy of Guangdong and increase the welfare of its people.
Guangdong is privileged to have such a beautiful landscape, with hundreds of historical sites and places of great interest to local people and foreigners alike. Our capital city, Guangzhou, is also known as "the city of flowers". Everywhere you look you will see flourishing plants and blossoming flowers overflowing with vigor.
The people of Guagdong are very friendly to visitors from anywhere. Whoever you are and wherever you come from, Guangdong people will greet you with the only language---Guangdong dialect.
Guangdong is also known as the Chinese capital of delicious food. There is an old saying that "The only best delicacies are in Guangdong.” Food from this province is internationally famous. Its variety of tastes, shapes and colors can satisfy even the most refined palette. I'm sure, the moment you seat yourself at a Cantonese banquet, your appetite will naturally become keen and eager to taste all the numerous delicacies of the region. Here are but a few I will mention in passing: steamed fish in ginger sauce, seasoned chicken, drunken shrimp, dance fish balls, fried jellyfish, roast suckling pig or duck, braised crispy chicken or squab, shark fin soup, moon cakes, refreshments and desert, and so many more. My mouth is watering just at the sound of these wonderful dishes.
I would like you all to know that there is truly nowhere in the world I would rather live and I invite you all to come discover the hidden treasures of my hometown. I would be glad to serve as your personal guide.
Thank you all.
广东欢迎您
我来自广东珠三角地区——一个可爱诱人的地方。
广东神奇美丽，俨如仙境;资源丰富，取之不尽。葱郁的群山栖息着无数的鸣禽候鸟，肥沃的土地培育着营养丰富的稻谷和健康宜人的水果。
珠江河蜿蜒曲折，河水晶莹剔透，孕育着品种丰富的水产。所有这些自然优势带来了广东经济的不断发展，带来了广东人民的幸福生活。
广东景色优美 ，有着许许多多的名胜古迹，深受当地人民和外国朋友的喜爱。广东的省会——广州，以花城著称。茂密的绿林、怒放的鲜花随处可见。
广东人民热情友好，无论你是谁，无论你来自何方，他们都会用同一种热情的语言欢迎你，那就是广东方言。
广东以中国美食之都著称。俗话说：“食在广东。”广东的饮食国际闻名，色香味俱全，令你胃口常开，让你禁不住想尝一尝这个地区的珍馐佳肴。在此我为你略举一二：罗汉斋、文昌鸡、片皮乳猪、醉虾、竹丝鸡、潮州冻肉、鼎湖上素、东江盐焗鸡、大良炒鲜奶等。
朋友们，广东是您理想的居住地。我诚挚邀请你们到广东来，我非常乐意成为你们的导游。
大学生英语演讲稿范文二：
I can hadle it
I can never forget the summer in 1996. I went through an extremity of despair due to my failure in the National College Entrance Examination. It seemed that my dream of being a university student would never come true. One evening my father came and told me the story of Steven Callahan, who was crossing the Atlantic alone in his sailboat when it struck something and sank. It was a miracle that he survived and was found 76 days later(the longest anyone has survived a shipwreck on a life raft alone). Later in his narrative he wrote these sentences “I tell myself I can handle it .Compared to what others have been through I’m fortunate”.
Hearing these sentences I felt something important struck me. I belived my life would mot be that bad and it was proved to be true. Later during my study in the university I always told myself “I can handle it” when my own goals seemed far off or when my problems seemed too overwhelming and every time I said it ,I always came back to my senses.
Now I work as an English teacher in a middle school. Whenever my students complain about their difficulties in study or want to give up, I will tell the same story of Callahan to them. I just want to make them believe they can handle their difficulties because their circumstances are only bad compared to something better. But others have been through much worse. Then they will build up fortitude.
So here, coming to us from the extreme edge of survival, are words that can give us strength. Whatever you’re going through, tell yourself you can handle it. Compared to what others have been through, you’re fortunate. Tell this to yourself over and over, and it will help you get through the rough spots with little more fortitude.
我能挺过去的
我永生难忘1996年的夏天。由于我在高考中的失利，我感到了极度的失望，我要成为一名大学生的梦想似乎是无法实现了。一天傍晚，我的父亲来给我讲了一个关于史蒂文·卡拉汉的故事，史蒂文独自驾驶着帆船横渡大西洋，途中船遇难下沉，但是他却活了下来并在76天后被人发现。(他是世界上遇海滩在救生艇中存活最长时间的人了)。后来卡拉汉在他的叙述中写到“我告诉自己一定可以挺过去的，跟别人的遭遇相比，我已经算是幸运的了”。
听了这些话，我被深深地震撼了，我相信我的生活不会太差而事实也证明了这一点，后来我得到了进入大学学习的机会，在大学学习期间，当我觉得自己的目标似乎遥不可及或者我遇到了似乎无法解决的问题时，我就勉励自己说“我能挺过去的”而每每念及这句话，我总能有所醒悟。
现在我在一所中学教英语，每当学生们报怨学习的困难或是想放弃时，我就给他们讲卡拉汉的故事，我就是想让他们相信他们可以从困难中挺过去的，因为困境都是相对而言的，有些人比我们更不幸，然后他们就会在自己心中建立起永不放弃的信念。
从这个大难不死的故事中，我们学到了能给予我们勇气与力量的话语，无论你遭遇了什么，都要对你自己说：一定能挺过去的。与其他人的不幸相比，你已经算是很幸运了，要一遍一遍地用此话鼓励自己，这个信念会使你更有信心渡过难关。