Passage Summary: Rockets need short nozzles for the start of the trip and long ones for the end to be super efficient. Therefore, they have to carry both types of nozzles.

Conclusion: To achieve maximum efficiency during their entire flight, all rockets must be equipped with both short and long nozzles.

Reasoning: Short nozzles are most effective in high-pressure low altitudes, while long nozzles are most effective in low-pressure high altitudes.

Analysis: The argument assumes that a rocket must have two distinct, separate nozzles to satisfy the efficiency requirements of different altitudes. It overlooks the possibility of a single, adjustable nozzle that can change its length or shape as the rocket ascends. To find the necessary assumption, look for an answer that addresses the lack of a 'variable' nozzle or the necessity of having both specific types present. If a rocket could just 'morph' its nozzle, the conclusion that it needs 'both' (implying two) would fall apart.