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问题 选择题

夏日炎炎，人们总喜欢躲在大树的阴影下乘凉，树阴的形成是由于（　　）

A．光的直线传播

B．光的漫反射

C．平面镜成像

D．光的折射

答案

光是沿直线传播的，所以遇到障碍物就会形成影子，所以B、C、D不符合题意；

故选A．

问答题

如图，设椭圆

（Ⅰ）求直线y=kx+1被椭圆截得到的弦长（用a，k表示）

（Ⅱ）若任意以点A（0,1）为圆心的圆与椭圆至多有三个公共点，求椭圆的离心率的取值范围.
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单项选择题

Questions from 36 to 40 are based on the following passage: Against this background, the WTO faces several daunting challenges. The first is to continue bringing down tariffs on traded goods. Average penalties have fallen steadily since the GATT’s formation but even the most open economies retain lofty barriers: for instance, America still charges a tariff of 14.6% on import of clothing, five times higher than its average levy.Resistance to tariff cuts is pest in agriculture. According to Tim Josling, a trade expert at Stanford University, tariffs and other barriers on farm goods average a crippling 40% worldwide and create distortions that “destroy huge amounts of value”. A new set of global farm talks is planned to start in 1999. At the least, you might think, these could lock in impressive reforms in Latin America and encourage further watering-down of the European Union’s Common Agricultural Policy. But they will prove difficult: squabbles over agriculture almost sank the Uruguay round.

Where do impressive reforms lock in according to the passage（）

A．America

B．Asia

C．Latin America

D．Africa
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