Final answer:
Martian civilization stopped asking themselves if they had the discipline to value the future more than the present.
Step-by-step explanation:
The question that Martian civilization stopped asking themselves is "Do we have the discipline to value a distant and unknown future more than we value ourselves and our own time?"
Bradbury illustrates this important theme in the context of Spender realizing that the Martian civilization thrived for a long time because they were able to prioritize the future over the present.