Answer:
1) Ella me (I.O) lo (D.O) regaló.
2) ¿Me (I.O) las (D.O) enviar?
3) Te (I.O) la (D.O) guardamos.
4) Yo se (I.O) lo (D.O) vendí
5) Roberto se (I.O) las (D.O) comió
Step-by-step explanation:
I.O = Indirect object, D.O = Direct object.
Usually (not always) the I.0 object can accept a prepositional complement in the phrase. Ex: Yo le compré un coche, Yo le compré un coche a él ("le" and "a él" being both I.O).
The direct object pronoun can usually be substituted by the D.O itself, so you can use that in your advantage. Ex: Ella lo compró, Ella compró un coche ("un coche" substituting "lo" here).
Also: "Se" is the same as "le" but it is used before any D.O pronoun (Ex: "lo") to avoid cacophony.