Final answer:
The statement is true; magnetic fields are responsible for the formation of sunspots on the Sun, which are cooler and darker regions on the solar surface.
Step-by-step explanation:
The statement that magnetic fields cause visible structures such as sunspots on the Sun is true. Sunspots are large, dark areas on the Sun's surface that are cooler and appear darker than their surroundings. The temperature difference is considerable, with sunspots being about 3800 K compared to the surrounding areas at about 5800 K. Magnetic fields play a critical role in the formation of sunspots. Studies of the Zeeman effect in sunspot spectra reveal strong magnetic fields within these regions. Furthermore, sunspots often occur in pairs that correspond to the north and south magnetic poles. The polarity of the leading and trailing spots in sunspot pairs is typically opposite, and this can be explained by the concept of magnetic loops protruding from the sun's surface. The intense magnetic fields in sunspots suppress the convective motion of hot gases, which normally transport heat to the sun's surface, resulting in cooler, darker spots.