设函数y=f(x)y = f(x)y=f(x)在点x=x0x = x_0x=x0处可导,且x=x0x = x_0x=x0为极值点,则f′(x0)=f'(x_0) =f′(x0)=( ).
(A)-1
(B)0
(C)1
(D)2
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