已知曲线y=f(x)y = f(x)y=f(x)在点(2,−1)(2, -1)(2,−1)处的法线斜率为1,则f′(2)=f'(2)=f′(2)=( )。
(A)−1-1−1
(B)222
(C)111
(D)12\dfrac{1}{2}21
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