jabhatta@umail.iu.edu
Really good question! And yes...that's one thing that tends to be a big difference between Assumption questions and Strengthen questions, that in Assumption questions the correct answer is
necessary in order for the rest of the argument to hold. So often/usually (I'll stop just short of saying "always" since that's so hard to prove, but man I'm having a hard time thinking of when it wouldn't be...), the right Assumption answer
must be true in order for the rest of the stimulus to also hold true. And that means that you could view the correct Assumption answer also as a valid Inference because it meets that same Must Be True standard that Inferences need to.
Here, if we were to take "if a person chooses to walk rather than drive, there is one less vehicle emitting pollution into the air than there would be otherwise" and "if people would walk whenever it is feasible for them to do so, then pollution will be greatly reduced" as facts, then the fact that pollution would be
greatly reduced (compared to now) means that currently not everyone who could walk rather than drive is walking, so that would mean that (E) has to be true.
And I think a big takeaway for future questions - correct Assumption answers are necessary premises in order for the argument to hold, so they "must be true" for the argument to work. So "must be true" is a great standard to hold these answers up to.
That's also why the Assumption Negation Technique works so well particularly when the answer isn't readily obvious - it forces you to consider what would happen to the argument if the correct answer were not true (if it failed the "must be true" standard). Correct Assumption answers are critical to the validity of the argument.