Question

which sentence uses a different grammatical structure than the others?
after a long day away, we arrive home to two hungry pups.
after so many hours alone, our pooches are ready for some love.
after the dogs eat, we usually take them out for a long walk.
after about an hour, everyone is prepared for a slow walk home.

Explanation:

The first, second, and fourth sentences use a prepositional phrase starting with "After" followed by a noun phrase (a long day away, so many hours alone, about an hour). The third sentence uses "After" followed by a dependent clause (the dogs eat) with a subject and a finite verb, making its grammatical structure distinct from the others.

Answer:

After the dogs eat, we usually take them out for a long walk.