已知函数f(x)=x3+ax2+bx.若y=f(x)的导数f′(x)对x∈[-1,1]都有f′(x)≤2,则ba?1的范围( )A.(-2,1]B.(-∞,-2)∪[1,+∞)C.(12,1]D.[-2,12]