Rocket engines are most effective when exhaust gases escape from their nozzles at the same pressure as the surroundin...

Irina on October 17, 2019

@hannahnaylor5,

The issue with (D) is that it says "to work effectively," whereas the argument concludes that to "work most effectively," which are not equivalent. It is possible for an engine to work effectively but still not at the highest possible effectiveness/ efficiency. (B) is a necessary assumption because the long nozzle is most effective in this upper atmosphere, but if the rocket never passes through this atmospheric layer, we could not conclude that to work most effectively though their ascents, all rockets must have both - as in this scenario only the short nozzle would be needed. Hence (B) is necessary for the conclusion to follow logically.

Let me know if you have any other questions.