The most fitting option for the empty space would depend on the context of the surrounding text. However, if the context is about a character's motivations or a significant aspect of the narrative, option C might be the most relevant choice, as it introduces a personal conflict that could drive the story forward.
So the complete thought could be: C. Thomas's wife and daughter are unhappy on Earth.
This option suggests a familial conflict that could impact Thomas's decisions or actions, making it a significant element of the narrative.