Question

which sentence or sentences have correct parallel structure?
before becoming involved in animal-assisted therapy, a dog must be able to sit on command, stay until released, and obey other basic instructions.
before becoming involved in animal-assisted therapy, a dog must be able to sit on command, to stay until released, and to obey other basic instructions.

Explanation:

Parallel structure requires consistent grammatical form for linked items. The first sentence uses base verbs ("sit", "stay", "obey") after the shared "be able to", which is parallel. The second sentence uses the repeated infinitive marker "to" for each verb ("to sit", "to stay", "to obey"), which is also a valid parallel structure.

Answer:

1. Before becoming involved in animal-assisted therapy, a dog must be able to sit on command, stay until released, and obey other basic instructions.
2. Before becoming involved in animal-assisted therapy, a dog must be able to sit on command, to stay until released, and to obey other basic instructions.