Final answer:
The passage suggests that humans could have detected an alien threat earlier if they had more advanced learning and technological capability, as the Martians' mathematical learning and strategic planning were superior.
Step-by-step explanation:
The idea that is BEST supported by the last paragraph of the passage is that the impending events could have been prevented if humans were more advanced in their learning. The reference to the Martians' superior mathematical learning and the subtlety of their descent suggests that a greater understanding and advancement in human learning might have allowed for earlier detection of the threat. Moreover, the mention that Earth's instruments were not sufficient to detect the trouble early enough reinforces the notion that technological advancements could have altered the outcome.
The passage does not suggest that communication with other planets would have prevented the threat or that the Martians' planning was flawed—instead, it indicates their planning was nearly perfect. It also doesn't imply that humans would have been better prepared in an earlier era; rather, it hints at a lack of preparedness in the face of alien technology.