Self-study
A new gardening rake with an S-shaped handle reduces compression stress on the spine during the pull stroke to about one-fifth of what it is with a straight-handled rake. ██████ ███ ████ ███████ ████████ ███████████ ██████ ██ ████ █████ ████ ████ ███ ███ ████ ████ ████ █ ████████████████ █████ ███████ ███ ████ ██████ ███ ███ ████ ██████ ████ █ ████████████████ ████ ████████ ██████ ███████████ ██████ ██ █████ ███████ ███ ███████████ ██████ ██████ ███ ████ ██████ ████ ███ ███ ████ ██ █████ ███ ██████ ██████ ██████████ ████████████████ █████ ███ ██████ ████ ███ ███ █████ ███ ██████████ ████ ██ ██████ ███████
Objective: Identify a Sufficient Assumption
The argument concludes that straight-handled rakes have a lower risk of spinal injury compared to new S-handled rakes. We reach this conclusion by comparing the compression stress on the spine using both push and pull strokes with each rake. With straight-handled rakes, neither push nor pull strokes produce enough compression stress to cause injuries. With S-handled rakes, push strokes produce five times more compression stress—enough to risk injury—while pull strokes produce five times less compression stress.
Boiling this down, the argument shows us that S-handled rakes have a greater risk of spinal injury from compression stress during push strokes compared to straight-handled rakes. That's much more specific than the conclusion that straight-handled rakes have a lower spinal injury risk overall. So to guarantee the conclusion, we're looking for an assumption that there are no other risk factors for spinal injury when using rakes.
20.
The conclusion above is properly █████ ████ ███ ████████ █████ ██ █████ ███ ██ ███ █████████ ██ █████
a
Compression stress resulting ████ ███████ ██ ███ ████ █████ ██ ████████ ██ ███ █████ ████ █████ ██ █ ██████ ██ ███████
(A) tells us that the argument doesn't overlook any other risk factors, which is the sufficient assumption we need. The only risk the argument attributes to S-handled rakes is from compression stress during push strokes. Assuming that's the only possible risk guarantees the conclusion that S-handled rakes have an overall higher risk of injury.
b
Raking is a ████████ █████ ██ ██████ ██████ █████ ██████████
The argument is only talking about comparative risk, so it doesn't matter how common spinal injuries from raking are in an absolute sense. No statement about absolute frequency could guarantee the argument's comparison between straight-handled and S-handled rakes.
c
The redesign of █ ████ ██████ ███████ ██ █ ███ ████ ██ ███████████ █████ █████ ████ ██ ██ ███████████████ ██ ███████
(C) goes off in a different direction from the argument, which doesn't discuss efficiency or the general merits of tool redesign. The argument is specific to a comparison of injury risk between straight-handed and S-handled rakes; a broad principle about what's usually true of tool redesigns doesn't make the argument properly drawn.
d
A garden rake ███ █████ ██ ████ ██ ████ █ ███ ████ ███ ███ ███████ ████ ████ ████ ███ ████ ████████
(D) makes an important mistake. The whole problem with S-handled rakes is in the push strokes, so saying there's a limit on push strokes doesn't even strengthen, let alone guarantee the argument.
e
It is not ████████ ██ ██████ █ ██████ ████ ████ █ ██████ ████ ██ █████ ████ ████████ ██ █████████
The argument compares two specific rake types, so it doesn't matter whether those are the only possible rake types. The existence or nonexistence of other rakes has no bearing on whether S-shaped rakes are really more dangerous.