Final answer:
The best word to complete the sentence is 'jugando' and it means 'playing' in English.
Step-by-step explanation:
The best Spanish word to complete the sentence is jugando.
The sentence 'Mi hermana está con el perro' translates to 'My sister is playing with the dog' in English.
Here, we need to use the present participle form of the verb 'jugar,' which is 'jugando,' to indicate an ongoing action. So the correct sentence is 'Mi hermana está jugando con el perro.'
Learn more about Word completion in Spanish