The footprints left on the Moon by astronauts will remain there for at least one hundred million years.
Why it is true
There is no wind or water on the Moon to cause erosion. The only thing that will very slowly erase them is the continuous impact of micrometeorites and solar radiation over geological eras.
Source: NASA
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.