Which sentence contains correct punctuation?

in some areas-the deserts of arizona and mexico, for example-cacti are native.
in some areas—the deserts of arizona and mexico, for example—cacti are native.
in some areas [the deserts of arizona and mexico, for example] cacti are native.

explanation:

the intellectual community is a place like a university where people with high marks, or original thought or an outstanding interest in something gather. they take classes together. they discuss things. they argue sometimes, and not always in a friendly way. but if they argue, it is because they are passionate about something, and there is nothing the matter with that.

lately i've been hearing rumors that it is not the way it was when i went to school. the one thing all schools used to have was free speech. the 1st amendment rights were sacred. now i'm hearing they are not. students can be reported and disciplined for giving an off the wall opinion.

that is shameful.

intellectual ideas are meant to be discussed. they are meant to be chewed up and worked on. that is the primary responsibility of every intellectual community. if that is not the way it is, then that is not a school to go to.

social media, in my opinion, and this is just an opinion. i wouldn't take it too seriously, complicates everything to do with human communication. you can want to share things and others feel they have the right to be very critical or sarcastic or mean about what you share. lack of respect is an immeasurable intolerable condition and social media abounds with that sort of thing.

one of the things i really like about is how careful people are because they must have some idea that the mods are exactly what the word says they are. they police this board very well, and what is so remarkable about them is that they are no older than the average grade 12 student.

my hat goes off to them (which means i respect them quite a bit).