Alive or not
Look at Figure 1.2. It will be clear which ones show something that is living and which show something that is non-living. What characteristics define whether something is 'alive' or not? Make a checklist that you could give to our friendly alien so they could use it to establish whether something is living or not.
Now you have reminded yourself of the characteristics of living things, How could you use these to explain to an extra-terrestrial that stalagmites growing in a cave are not living, yet corals are?
Background information
Stalactite and stalagmite
Coral reefs