Which of these give an expression for the mean of a discrete distribution?

• A. ( int_{- infty}^{ infty} xf(x)dx )
• B. ( sum_{i=1}^{ infty} x_i p(x_i) )
• C. ( sum_{i=1}^{ infty} (x- mu)^2 p(x_i) )
• D. ( int_{- infty}^{ infty} (x- mu)^2 f(x)dx )