According to the Brønsted theory, classify each reactant and product in the given reaction as an acid or base:
a) H3PO4: acid, C6H5OH: base
b) H3PO4: base, C6H5OH: acid
c) H3PO4: acid, C6H5O-: base
d) H2PO-4: acid, C6H5OH: base