Final answer:
The frequency word that best completes the sentence is 'con frecuencia', meaning frequently.
Step-by-step explanation:
In this sentence, the frequency word or phrase that best completes it is con frecuencia, which means 'frequently' in English. The sentence refers to the need to clean and vacuum because the dog is very dirty. The phrase con frecuencia indicates that the cleaning and vacuuming needs to be done regularly or with frequency.
Learn more about Frequency word completion in Spanish sentence