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问题 选择题

双曲线x2-y2=1的左焦点为F，点P为左支下半支上任意一点（异于顶点），则直线PF的斜率的变化范围是（　　）

A．（-∞，0）

B．（1，+∞）

C．（-∞，0）∪（1，+∞）

D．（-∞，-1）∪（1，+∞）

答案

由题意条件知双曲线的渐近线倾斜角为45°，

当点P向双曲线右下方无限移动时，直线PF逐渐与渐近线平行，但是永不平行，所以倾斜角大于45°；

当点P逐渐靠近顶点时，倾斜角逐渐增大，但是小于180°．

所以直线PF的倾斜角的范围是（45°，180°）．

由此可知直线PF的斜率的变化范围（-∞，0）∪（1，+∞）．

故选C．

单项选择题

Are you a man or a mouse When people ask this question they want to know (1) you think you are a (2) person or a coward. But you will never really know the answer to this question (3) you are tested in real life. Some people (4) they are brave but when they come face to face with real (5) , they act like cowards. Others think of themselves as cowards, but when they meet danger, they act like (6)

Lenny had always thought of himself as a (7) person. He got worried before examinations. He worried about his job and health. All he wanted in life was to be safe and healthy. (8) , on January 15th, 2002, a plane crashed into the Potomac River in Washington. Lenny went to the river to see what was happening. He saw a woman in the (9) water. Lenny did not feel afraid. He kept very (10) and did a very dangerous thing. He jumped into the Potomac, (11) to the woman, and kept her head (12) the water. Seventy-eight people died that day. Thanks to Lenny, it was not (13) .

When you are in a very (14) situation and feel afraid, the body automatically produces a chemical in the blood. The chemical is called adrenalin. (15) adrenalin in the blood system, you actually feel per and per and are (16) to fight or run away. However, when you are absolutely terrified, the body can produce too much adrenalin. When this (17) , the muscles become very hard and you find you (18) move at all. You are then paralyzed with fear. This is (19) when we are very frightened, we sometimes say we’re "petrified". This word comes from the Greek word "petros", which means "stone". We are (20) frightened that we become stonelike.

15（）

A.With 

B.Without 

C.For 

D.Like
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单项选择题

宋代福建作家（）编有《西昆酬唱集》，是“西昆体”主要作家之一，在当时文坛产生了广泛的影响。

A.郑文宝

B.杨亿

C.黄昇

D.杨徽之
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