Answer:
A). Isolation.
Step-by-step explanation:
The theme or the 'underlying message' that Franz Kafka discusses in the given excerpt would be 'isolation' as it discusses the pain and suffering that Gregor suffers after being transformed into a cockroach. He 'lost his mobility' and 'reduced to the condition of an ancient invalid.' He was completely alone and shattered. He is broken completely and had no one to talk to. He was deteriorated to such a miserable condition that it took him too long to crawl his room. He was lying in utter darkness with no one to share his thoughts and he could only listen to the conversations of his family at the dinner table from a distance. Thus, these situations clearly display that Gregor was completely isolated and broken and that is the central idea that Kafka is conveying. Thus, option A is the correct answer.