Final answer:
The answer to what 'Defensive Magical Theory' says about counter-jinxes is not provided among the choices, and without the specific content, a definitive answer isn't possible. Generally, counter-jinxes in the Harry Potter series are defensive spells used to neutralize jinxes.
Step-by-step explanation:
The student's question concerns a specific topic within the fictional subject matter of the Harry Potter universe, more precisely the book 'Defensive Magical Theory.' The correct answer to what 'Defensive Magical Theory' has to say about counter-jinxes is not provided in any of the choices. Instead, it refers to a topic that would likely fall under magical defense. Given the fictional nature of the material, and without a direct reference to the content of 'Defensive Magical Theory,' it's not possible to provide a definitive answer to the student's question. In general, within the Harry Potter series, counter-jinxes are typically presented as defensive spells meant to protect against jinxes. These defenses are an integral part of magical combat and are taught as a part of a wizard's education in defensive magic. However, without specific text from the book 'Defensive Magical Theory,' we cannot ascertain the book's stance on the efficacy or requirements for using counter-jinxes.