问题 选择题

已知p:直线l1:x-y-1=0与直线l2:x+ay-2=0平行,q:a=-1,则p是q的(  )

A.充要条件

B.充分不必要条件

C.必要不充分条件

D.既不充分也不必要条件

答案

当命题p成立时,直线l1:x-y-1=0与直线l2:x+ay-2=0平行,故两直线的斜率相等,∴a=-1.

当q成立时,a=-1,直线l1:x-y-1=0与直线l2:x+ay-2=0平行,故命题p成立.

综上,p是q的充要条件,

故选 A.

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                                                                   Wanted!

                                                     4 middle school students

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      假定你叫李华,愿意应聘。请写封电子邮件,介绍自己,并说明你愿意应聘的理由。词数110左右。开头已写好,不计入总词数。

       Dear Emesto and Stasi,

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       Yours sincerely

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