By definition, we have to:
The pedestrian is a person who, without being a driver of a vehicle, transits on foot through public spaces of the city.
We use this definition to complete the given sentence.
We have then:
El peatón es la persona que camina en la acera.
The translation of the sentence in English is:
The pedestrian is the person who walks on the sidewalk.
Answer:
c. el peatón
El peatón es la persona que camina en la acera.