Final answer:
The fact that Mars has volcanoes implies it has a molten interior capable of sustaining geological activity, though less compared to Earth due to its smaller size.
Step-by-step explanation:
The existence of volcanoes on Mars suggests that the planet has a geologically active interior. The size of a planet significantly impacts its geological activity; larger planets retain internal heat longer, fueling volcanism and tectonic activity. Mars, being smaller than Earth and Venus, has a lower level of geological activity, but it is still more active than the Moon. This suggests that Mars has a molten interior, which has allowed it to sustain volcanic activity over an extended period. For instance, the Tharsis bulge, characterized by several enormous volcanoes including Olympus Mons, indicates continuous volcanic activity that may have occurred in intervals up to the present era.