“Sadly, the first few closest stars are not visible to the naked eye at night, which means we can’t see them while we’re stargazing from our homes or backyards.” - What does the phrase the "NAKED EYE" mean in the sentence above?

It basically means you can't see it with your normal eyesight. You have to use a telescope, or some other science instrument.

Explanation:

balearic sea - is a body of water in the mediterranean sea around the balearic islands. baltic sea - is a mediterranean sea of the atlantic which is enclosed by scandinavian and baltic countries. barents sea - is a marginal sea in the artic ocean located off the northern coast of norway and russia.

the answer is:

c. economic output