Right answer:
a. hable
The sentence:
Pido que mi madre hable con mi tía
Stands for the subjunctive mood. We use the subjunctive to express desires, doubts, the unknown, the abstract, and emotions. Subjunctive sentences often have parts linked by a relative pronoun (que, quien, como). Here we use que. On the other hand, hable is the conjugation of the verb hablar for the third person singular in the subjunctive mood.