题目

阅读短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。 Moscow city authorities have begun using comics (漫画) with characters fromRussian fairy tales to explain to migrants (移民) how they should behave.They say a 100-page guide is needed to keep a positive image of thecity and could help reduce tensions between natives and migrants.But critics have pointed out that foreign migrants and natives may be regardedas antagonists in the manual (手册). Russians and migrantshave repeatedly flooded in Moscow recently. Many migrants from ex-Sovietrepublics in C已知圆，直线:x=6，圆与轴相交于点（如图），点P(-1,2)是圆内一点，点为圆上任一点（异于点），直线与相交于点．（1）若过点P的直线与圆相交所得弦长等于，求直线的方程；（2）设直线的斜率分别为，求证： 为定值.