I'm not exactly sure what you're asking, but I'll try.
The answer is "compro" because it's past tense. I should know, I speak both Spanish and English.
Answer:
1. Las
2. La
3. Una
4. Un
5. Unos
Explanation:
The correct article is indicated taking into account if the noun is pural or sigular and if it is masculine or feminine.
Yo llegue temprano a la oficina esta manana.
Ella preparo el cafe ayer.
Todas las mananas, Maria y Marta caminan por el parque.
Nosotros descubrimos el dinero anoche
