Complete the alien's postcard to its home planet by choosing the correct word to describe human habits.

I noticed that most humans sleep at night, though a few stay awake to stare at glowing screens.

I still have no idea why they drink hot bean water every single morning.

My research shows that absolutely all Earthlings need oxygen to survive, without a single exception!

I noticed that most humans sleep at night...

Since "a few stay awake," we know it isn't 100% of humans. "Most" correctly describes the large majority.

I still have no idea why they drink hot bean water...

"To have no idea" is a common phrase meaning to not understand something at all.

...absolutely all Earthlings need oxygen to survive, without a single exception!

"Without a single exception" means 100% of the group, so "all" is the correct choice.