Trennbar verbs in the Prepositions unit
I noticed that trennbar verbs (separable verbs) like vorleben and nachdenken were split in the questions in the Prepositions unit, and the unit gives the impression that the preposition could exist without the verb. Neither vorlesen nor nachdenken appeared in the vocabulary list for the unit, even though I'd never encountered them on Duolingo before.
I am using Duolingo to brush up on my German, and so I understood the split. But it still took me a little thinking to figure out. Someone who had never studied would not only be confounded, but would not recognize that vorlesen and nachdenken were the verbs in the sentence, rather than lesen+preposition and denken+preposition. A unit on trennbar verbs really should come first.