Self-study
Support If a person chooses to walk rather than drive, there is one less vehicle emitting pollution into the air than there would be otherwise. █████████ ██ ██████ █████ ████ ████████ ██ ██ ████████ ███ ████ ██ ██ ███ ████ █████████ ████ ██ ███████ ████████
Argument Breakdown
The author concludes that if people would walk whenever feasible, then that would greatly reduce pollution. Why? Because if someone walks instead of driving, then that avoids one car's worth of emissions. In other words, because walking rather than driving reduces pollution, walking whenever feasible would reduce pollution.
Objective: Identify a Necessary Assumption
Notice that the author treats two ideas as interchangeable: walking whenever feasible and walking instead of driving. This means the author must assume that it is sometimes feasible for people to walk when they currently drive. Not only that, but this must be common enough to have the potential to significantly reduce car pollution.
We know this assumption is necessary because the argument falls apart when we negate it. If people already only drove when it wasn't feasible to walk, then walking whenever feasible couldn't make any difference.
8.
Which one of the following ██ ██ ██████████ ██ █████ ███ ████████ ████████
a
Cutting down on █████████ ███ ██ ████████ ██ █ ███████ ██ █████
The author is only claiming that one strategy could reduce pollution, so whether there are other ways to reduce pollution isn't relevant. The argument holds up regardless of whether there are other possibilities.
b
Taking public transportation ██████ ████ ███████ ██ ███ ██████ █████████
The author is only concerned with the comparison between walking and driving. It's not necessary to make any assumptions about other modes of transportation, because they make no difference to the argument.
c
Walking is the ████ ████████ ███████████ ██ ███████ ████ ███████ ██ █ █████████ ██ ██████████
Like (B), (C) appeals to our common-sense knowledge that there are other, cleaner modes of transportation than driving. But other modes of transportation aren't relevant to the argument even though they're very relevant to real-life emissions reduction strategies. The argument has a narrow focus on the claim that walking rather than driving would reduce emissions.
If the author claimed that walking was the only way to reduce car emissions, then this assumption might be necessary. But the possibility to reduce emissions in other ways doesn't affect the argument, which is just about what would happen if people walked whenever feasible.
d
There are people ███ █████ █████ ███ ███ █████ █████
These people would have no opportunity to further reduce emissions by walking instead of driving, so they aren't relevant to the argument. The author is only talking about people who sometimes drive, so we don't have to assume the existence of any other group.
e
People sometimes drive ████ ██ ██ ████████ ██ ████ ████████
For walking whenever feasible to have any impact on pollution, it has to be the case that people sometimes drive when they could walk; otherwise, walking whenever feasible wouldn't reduce driving at all. Because (E) must be true for the argument to function, we know it's necessary to assume.