The first horse like animal from which the modern horse Equus has evolved , Oligocene was the

Question

$\begin{array}{1 1} (a)\;\text{Pliohippus from Pliocene} \\ (b)\;\text{Eihohippus from Eiocene} \\ (c)\;\text{Merrychippus from Myosin} \\ (d)\;\text{Mesohippus from Eiocene} \end{array} $