Dalia: ¿qué le diste a tu papá por su cumpleaños? isabel: le un reloj a mi papá.

The correct answer is option c. di.

Explanation:

The dialogue is referring to what Isabel gave her dad for his birthday, so the correct verb to use is "to give" ("dar" in Spanish). Now, in order to conjugate correctly the verb, we have to do it in the first person singular, because Isabel is talking directly of what she did. And, it has to be in past simple, because Dalia is asking for an event that Isabel did in the past. Now, the conjugation of "dar" in the past simple for the first person singular is "di". Therefore, the correct answer is option c. di.

All other options are correctly conjugated in the past simple, but none of them are in the correct person and number. Option a. dio is for the third person singular; option b. diste is for the second person singular; and option d. dieron is for the third person plural.