The correct answer is D. It is the person or thing to or for whom the verb's action is done.
Use the system of elimination if you are unsure:
A is incorrect because a sentence that has a direct object doesn't have to have an indirect object as well. For example: I love books - here, books is the direct object but there is no indirect one
B is incorrect because they can. For example: I bought the book for myself. Here, the pronoun myself obviously ends in -self and is used as an indirect object.
C is also incorrect because objects (both direct and indirect ones) are always found after the verb.