I love how this course educates on what Esperanto is as we go along.
So in this context either "ĉirkaŭ" is a valid replacement for "tra" or "around" is a valid possible translation of "tra".
I think so. In French, for instance, you can say either "à travers le monde" ("tra la mondo") or "autour du monde" ("cxirkaux la mondo"), and Esperanto was heavily influenced by French.
why is 'persons around the world. ....' not correct?
These days "persons" sounds a little awkward in English. It's still valid, but very rarely used in common speech. We prefer to use "people".
That said, I don't think your answer is technically incorrect, so it may be worth reporting your suggestion.
Thank you for the answer.
The power of suppletion!
Why is "People throughout the world are speaking Esperanto" incorrect? It seems in other examples "am/is/are do-ing" is more preferred than just "do/does"
Because that would mean that people throughout were speaking Esperanto at the moment. "Speak Esperanto" means that you know Esperanto and can speak it.
It rejects 'humans'?
Perhaps "people" is meant to include "non-human persons"?