56. Which of the following would be the best title for the text?

   A. Codeine: A New Medicine        B. Chocolate May Cure Coughs

   C. Cough Treatment: A Hard Case    B. Theobromine Can Cause Coughs

答案：B。本文开篇就道明了主题：巧克力中的某种成分可以治疗咳嗽，下文始终围绕这个主题来展开说明。

2) 文尾归纳要点，提出建议，以概括主题。即归纳法写作方式。如：

A human body appears to be rather soft and delicate, compared with that of a wild animal, but it is actually surprisingly strong. In deed, its very softness and looseness is an advantage; it makes a man good at moving about movement of all living things of his own size, because he can do so many different things with his limbs. Man’s games show how he can control his own body. No other land creature can swim as skillfully as man; none has such varied grace; very few live as long as he; none is so strong in its natural resistance to disease. Therefore man has a great advantage in his battle against the risks of damage and death that threaten him.

3)文中。通常前面只提出问题，文中的主题由随之陈述的细节或合乎逻辑的引申在文中导出，而后又作进一步的解释、支持或发展。如：

Nothing is as useful as a flashlight in a dark night if a tire goes flat. Few inventions are so helpful to a child who is afraid of the dark. In fact, the modern flashlight brings light to many dark situations. Finding something in the back of a closet is easy with a flashlight in hand; a camper also needs one after the light of the campfire has been out.

4)首尾呼应。为突出主题，作者先提出主题, 结尾时再次点出主题，这种首尾呼应的写作方式较为多见。但前后表述主题的句子不是简单的重复，后面的表述往往有进一步引申或发展的意味。如：

（首段）Shu Pulong has helped at least 1000 people bitten by snakes,“It was seeing people with snakes bites that led me to the career. ”She said…

（尾段）“The sad story touched me so much that I decided to devote myself to helping people bitten by snakes.” Shu said.

5) 无主题句，即主题句隐含在全文中，没有明确的主题句，必须根据文中所提供的事实细节进行全面考虑、综合分析，然后找出共同的东西，归纳成一般概念。必须注意的是，既不能以偏概全，也不能在概括时过于宽泛，要恰如其分。如：

Joshua Bingham studied 4 years at the University of Paris and decided to leave his graduation. He transferred to the University of Berlin and graduated with honors. Harvard Law School and, later, Boston College provided him with an excellent legal background. He is presently a corporation lawyer in Miami, Florida.

Q: What is the main idea of the passage?

A. How Joshua Bingham became a lawyer.   B. Bingham is a diligent student.

C. Joshua Bingham received an excellent education.

D. A good lawyer needs good education.

[分析]此文没有主题句。全篇共四句，只陈述了四个细节性的事实。因此就答案本身看个个都对。读者只能将所有的细节（details）综合起来进行逻辑推理，才能构成一个没有言明的主题思想(unstated main idea)。由于文中主要涉及了Joshua Bingham接受教育的情况，即作者想告诉我们的是：Joshua Bingham接受过良好的教育，所以答案是C。

除了以上主题句呈现的常见形式外还要注意标志词。文章或段落的主题句常常会出现在一些标志性的提示后。如：on the whole, as a result，in short，therefore，thus… I agree with the opinion that…; Given all these points above, I would support the idea that…; For all the reasons mentioned above, I would prefer...

存在，求出符合条件的一个；否则，说明理由．

（Ⅲ）对于区间（1，2）中的任意常数，是否存在使成立？若

（Ⅱ）若在其定义域内是单调函数，求的取值范围；

    （Ⅰ）若，求证：；

已知函数，，其中无理数．

22．（本小题满分15分）

（Ⅱ）若直线与椭圆交于两点，且（为坐标原点），于点．试求点的轨迹方程．

（Ⅰ）求椭圆的方程；