One of the necessary and sufficient condition for a network function N(s)=p(s)/q(s) to be a transfer function is thatÂ

A) The coefficients of the polynomial p(s) and q(s) must be real and those for q(s) must be positive B) Coefficients of p(s) and q(s) must be real and positive C) Coefficients of p(s) must be positive and real but coefficients of q(s) can be negative also D) Degree of p(s) and q(s) may differ by either zero or one only