For any two complex numbers $\;z_{1}\;$ and $\;z_{2}\;$, what is the value of $\; Re(z_{1} z_{2}) $?

Question

$(a)\;0\qquad(b)\;Rez_{1}Rez_{2} - Imz_{1}Imz_{2}\qquad(c)\;Rez_{1}Imz_{2} - Imz_{1}Rez_{2}\qquad(d)\;Imz_{1}Rez_{2} - Rez_{1}Imz_{2}$