The number of telephone call \(N\) between two cities \(A\) and \(B\) varies directly as the population \(P_{A} P_{B}\) in \(A\) and \(B\) respectively and inversely as the square of the distance \(D\) between \(A\) and \(B\). Which of the following equations represents this relation?
A. \(N=\frac{k p_{A}}{D^{2}}+\frac{C P_{n}}{D^{2}}\) B. \(N=\frac{k p_{A} P_{\text {U }}}{D^{2}}\) C. \(N=k P_{A} P_{B}\) D. \(N= kDP _{ A }+ CDPB _{ B }\) E. \(N=k D^{2} P_{A} B_{D}\)
