"The teacher is asking the boys about something."

Translation: La instruisto demandas al la knaboj pri io.

[Camilyon]

Why woudn't "estas demandi" be correct?

[Luis_Domingos]

That's not proper Esperanto (there's a present progressive form in Esperanto - estas demandata - but I'm not sure if the Duo course covers that at all). For now all you need to know is that the present tense in Esperanto can be used for both present simple and present continuous in English.

[Camilyon]

Got it. Thanks! And yes, hopefully the Duo course covers it. Perhaps it is hidden in some of the other lessons. We will see.