"We travel through time with a time machine."
Translation:Wir reisen mit einer Zeitmaschine durch die Zeit.
mit triggers a dative object while durch triggers (here) an accusative object.
No. Prepositional phrases are not objects of a verb.
Prepositions take complements in a certain case but those noun phrases are not objects.
(And durch always takes the accusative case, not just here.)
So, I accidentally put my answer into future tense by throwing a werden in there, so I know why I got it wrong. BUT. Every other exercise in this series has wanted "eine Zeitreise machen" for travel through time. I'm not sure why it's suggesting "reisen... durch die Zeit" for this one. Any insight as to the preference for one over the other? **Note: It DOES ACCEPT "eine Zeitreise machen," it's just that it suggests the other, and doesn't do so for any other exercise with that expression that I can remember (which is why it became my go-to).