Help the confused alien complete its report to the mothership by choosing the correct phrase.

"Humans put tiny speakers in their ears and sit for hours just to _____ invisible sound waves."

The correct answer is listen to.

Because the sentence is about ears and sound waves, we need a verb related to hearing ("listen").

In English, when we actively pay attention to sounds, we use the collocation listen to + [the object]. We never say "listen at" or just "listen the sound waves."