Explanation: When two sine waves of the same frequency do not reach their maximum (peaks) or minimum (troughs) values simultaneously, it means there is a timing offset between them. This timing offset is precisely what constitutes a **phase difference**. The phase describes the position of a wave within its cycle (e.g., at 0, 90, 180, 270 degrees) at a given instant. If the waves are not aligned in their peaks and troughs, then a phase difference *does* exist (A). This condition is also commonly referred to as the waves being **out of phase** (C). They are "out of phase" because their cycles are not perfectly synchronized. Therefore, both statements A and C are correct descriptions of the scenario, making D the correct answer. Option B is incorrect because the described situation directly implies the existence of a phase difference.