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.
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Explanation:

Parallel structure requires consistent grammatical form for linked items. The first sentence uses base verbs (sit, stay, obey) after "be able to" (the initial "to" applies to all items). The second sentence repeats the infinitive marker "to" for each item (to sit, to stay, to obey), which also follows parallel structure. Both maintain uniform verb forms in the list.

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.