Which one of the statements below is true about mechanical waves? They must travel in empty space.
They can travel in a vacuum.
Both sound and light are examples of mechanical waves.
They require a medium to travel through.

Both sound and waves

Explanation:

Thank me later

b. latent learning (the word "latent" itself means something that exists but isn't obvious, only under certain conditions! )

the answer is to check all of them! they all apply well at least i think so!