Final answer:
A significant presence of impact craters on a volcano's surface indicates it has not been active for a long period, as eruptions would cover or alter craters.
Step-by-step explanation:
Evidence that a volcano has NOT been active for a long period of time would be the presence of a fair number of impact craters on its slopes. Such craters accumulate over long periods when the volcanic surface is not being renewed by eruptions, which would otherwise cover or alter existing craters.
For instance, Olympus Mons on Mars has very few impact craters, indicating its surface is relatively young and the volcano might still be active. In contrast, bodies like the Moon and Mercury with many craters are considered geologically dead, showing no recent volcanic activity.