1. Correct answer:
a. Jugábamos al tenis.
Jugábamos is the conjugation of the verb jugar that matches the first person plural (nosotros) in the imperfect. In general, the imperfect is used to talk about past actions, conditions, or events that occurred regularly or frequently or that were in progress in a moment in the past. So we used to play tennis in the past.
2. Correct answer:
b. Le
Le is the indirect object pronoun that matches the third person singular. An Indirect Object Pronoun is a person that receives the action of a verb indirectly. Its purpose is to tell you to whom or for whom something is done. So Ana receives the action of the verb to buy (comprar) here, so this action is being performed for her. Finally:
Le compró el libro a Ana