What is the expression for Fourier series coefficient ck in terms of the discrete signal x(n)?

• A. \(\frac{1}{N} \sum_{n=0}^{N-1}x(n)e^{j2πkn/N}\)
• B. \(N\sum_{n=0}^{N-1}x(n)e^{-j2πkn/N}\)
• C. \(\frac{1}{N} \sum_{n=0}^{N+1}x(n)e^{-j2πkn/N}\)
• D. \(\frac{1}{N} \sum_{n=0}^{N-1}x(n)e^{-j2πkn/N}\)