Answer:
D. ¿Quién conoce [a] María?
Glossary:
Conocer = To know
Conoce = He/She/It knows
Explanation:
The 2nd and 3rd sentence are totally incorrect, since the word "concoe" does not exist. The 1st sentence is grammatically incorrect, but the word "conocen" does exist (conocen = they know).
Hope it helped,
BiologiaMagister
