Final answer:
The word that best completes the sentence is "por" and it indicates the general direction or route of the action.
Step-by-step explanation:
The correct word that best completes the sentence "Prefiero caminar las calles." is por.
This word is used to express the concept of walking through the streets without specifying a destination or purpose.
For example, if you say "Prefiero caminar por las calles", it means "I prefer to walk through the streets". The word "por" indicates the general direction or route of the action.
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