Answer:
Prefiero caminar por las calles
Explanation:
The word which best completes this sentence is por. All the options ('de', 'a', 'para', 'por') are prepositions.
Prepositions indicate a relation between two words, they link words.
The translation of the sentence is 'I prefer to walk the streets' and the translation of the prepositions is 'from', 'to', 'for', 'for/by'.
