The derivative of digital function is defined in terms of difference. Then, which of the following defines the first order derivative ∂f/∂x= ___________ of a one-dimensional function f(x)?

• A. f(x+1)-f(x)
• B. f(x+1)+ f(x-1)-2f(x)
• C. All of the mentioned depending upon the time when partial derivative will be dealt along two spatial axes
• D. None of the mentioned