Passage Summary: It is too expensive to send building supplies to Mars, so we probably will not be living there anytime soon.

Conclusion: Establishing a human colony on Mars will not be financially practical.

Reasoning: Building a colony requires massive amounts of materials, and the cost of shipping those materials from Earth through space is prohibitively high.

Analysis: The author is assuming that the only way to get materials to Mars is by shipping them from Earth at a high cost. This creates a significant logical gap: what if we do not have to ship them? To make the conclusion follow, the argument must assume that there is no other viable way to obtain these materials. Look for an answer that rules out the possibility of sourcing or manufacturing these basic materials directly on Mars.