Final answer:
Most volcanic activity does occur along oceanic ridge systems where seafloor spreading takes place, hence the answer is true (A). This volcanism is associated with mid-ocean ridges, and while also significant, subduction zone and hot spot volcanism contribute to Earth's volcanic activity as well.
Step-by-step explanation:
Most of the volcanism on Earth indeed takes place along oceanic ridge systems where seafloor spreading occurs. This process happens primarily at divergent plate boundaries, where tectonic plates move apart from each other. As they separate, molten rock rises from the mantle to fill the gap, forming new oceanic crust. This volcanic activity is continuous and comprises the most voluminous on Earth. Thus, the statement that most volcanism happens along mid-ocean ridges is true (A).
Another significant area of volcanic activity is along convergent plate boundaries, where one plate subducts under another. This subduction leads to partial melting of the asthenosphere, which drives volcanism closer to continents. Additionally, there are hot spots, like the one under Hawaii, that are stationary areas of heat from the mantle causing volcanic activity far from plate boundaries.