Why Does Pyrrole Have a Lower PKa (Weaker Base) Than

Why does pyrrole have a lower pKa (weaker base) than pyridine or pyrimidine?

A) Because pyrrole is smaller and more compact and this prevents its lone pair from reacting as much.
B) Because pyrrole has less carbons and therefore the lone pair is more active.
C) Because pyrrole's lone pair participates in the delocalized electron cloud, while pyridine's and pyrimidine's lone pairs do not.
D) Because pyrimidine has more lone pairs than pyrrole does.