17.设二次函数y1=a(x-x1)(x-x2)(a≠0,x1=x2)的图象与一次函数y2=kx+b(k≠0)的图象交于点(x1,0),若函数y=y1+y2的图象与x轴仅有一个交点,则( )
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| A. | a(x1-x2)=k | B. | a(x2-x1)=k | C. | a(x1-x2)2=k | D. | a(x1+x2)2=k |