Which word best completes this sentence? prefiero caminar las calles.
de
a
para
por

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'.