Question

how are certain songs, smells, or familiar places like time machines?
they take us back to certain memories.
they allow us to change the past.
they give us the ability to travel backwards or forwards in time.
they keep us young.

Explanation:

Songs, smells, or familiar places can trigger memories (this is related to how sensory cues or familiar environments are linked to memory retrieval in psychology). Changing the past or actual time travel via these is not possible, and they don't keep us young. So the correct reasoning is that they take us back to certain memories.

Answer:

A. They take us back to certain memories.