He recommended ______ good dentist but _____ dentist does not have any openings for two months.

He recommended __ good dentist but _ dentist does not have any openings for two months.

A - the

The - a

The - the

None of these

"A good dentist" is used for the first general mention (indefinite article).

"The dentist" refers to the same specific person already introduced (definite article).