Complete the alien spy's observation log about Earthlings.

While general human behavior is baffling enough, ___ I have observed at this particular coffee shop seem utterly addicted to boiling hot roasted bean water.

The correct answer is most of the humans.

When referring to a specific, restricted group (the humans at this particular coffee shop), we must use most of the + noun (or another determiner like these or my).

"Most humans" is used for general statements about the entire species. "Most of humans" is grammatically incorrect because "of" must always be followed by a determiner or a pronoun.