18. ¿Mandas una tarjeta a tu amigo?
(Do you send a card to your friend?)
In the English sentence above, "a card" is the direct object, since it has no prepositions. However, "to your friend" is the indirect object, once it has the preposition "to", equivalent to "a" in Spanish.
A possible correct answer could be: "Sí, la mando para él."
"La", as a direct object, retakes the feminine term "tarjeta" - card -, and "él", masculine 3rd person singular pronoun, retakes the term "amigo" - friend -, being placed as indirect object.
19. ¿Haces la tarea para tu profesora?
(Do you do the homework for your teacher?)
In the English sentence above, "the homework" is the direct object, since it has no prepositions. However, "para tu pofesora" is the indirect object, once it has the preposition "for", equivalent to "para" in Spanish.
A possible correct answer could be: "Sí, la hago para ella."
"La", as a direct object, retakes the feminine term "tarea" - homework -, and "ella", feminine 3rd person singular pronoun, retakes the term "profesora" - teacher -, being placed as indirect object.