Which of the following condition is for polydisperse polymers?

Question

$\begin{array}{1 1}(a)\;\bar{M_w} > \bar{M_N}\\(b)\;\bar{M_w} < \bar{M_n}\\(c)\;\bar{M_w} = \bar{M_N}\\(d)\;\text{None of these}\end{array}$