曲线y=ax+bx2+Cx有拐点(1,2)处的切线斜率为-1,则常数a - ( ) , b = ( ) , c = ( )
A 2 , - 9 , 1
B.1 , - 9 , 8
C. 3 , - 9 , 8
D . 3 , - 1 , 0