(A): p-n-p transistor is faster than n-p-n transistor

(R): The mobility of electrons is greater than the mobility of holes

A  n-p-n transistor has electrons as majority charge carriers whereas the p-n-p transistor has holes as the majority charge carriers. The mobility of electrons is better than the mobility of holes. Mobility of electrons is more than hole, so as a result n-p-n transistors are faster than p-n-p that's why they are preferred.