La semana pasada compré una blusa nuevas y a mi mamá le encantó.
Explanation:
La semana pasada compré una blusa nuevas y a mi mamá le encantó. This means: Last week I bought a new shirt and my mom loved it. Both verbs are in the preterite. The options in the imperfect are semantically incorrect because the texts implies that the action was initiated and finished in the past. The imperfect could be used for an habit or indefinite action in the past, or a specific action that was interrupted by some other. For example:
La semana pasada compraba una camisa cuando mi mamá me llamó por teléfono (action interrupted by some other).
Compraba camisas para mi mamá siempre que era su cumpleaños (habit in the past).
