I believe the correct answer is D. Day in, day out, on the road.
This sentence shows a routine and repetitiveness that is not often appreciated in the modern world. People generally wake up, eat, go to work, then return home, rest, and go to sleep, and when they wake up the next day, the whole routine is repeated. This is what Kafka also wanted to portray in his work, which is why I believe D is the correct answer.
