Please explain

Please explain

@sharpen7 the argument here jumps from the likelihood of the push/pull stroke to cause injury to concluding that one rake is better at minimizing the risk of spinal injury in general. This is a Strengthen with Sufficient Premise so we are looking for an answer choice that 100% guarantees the conclusion. We can guarantee the conclusion here if the push/pull stroke compression stress risk of injury is the only risk of spinal injury posed by the rakes. Notice that this is exactly what (A) says, "Compression stress resulting from pushing is the only cause of injuries to the spine that occur as a result of raking." (C) on the other hand does not even strengthen this argument. The argument is not about whether the redesigned rake has resulted in a net gain of efficiency. This argument is about the relative risk of spinal injury caused by two different types of rakes. So (C) would be eliminated. Hope that helps! Please let us know if you have any other questions.

Why is it A though? Because they say that "compression stress resulting from PUSHING is the only cause of injuries to the spine that occur as a result of raking." However you can also get a spine injury from pulling so ??? I'm confused

Actually, @Ceci, the stimulus specifically says that "neither the push stroke nor the pull stroke with a straight-handled rake produces enough compression stress to cause injury." This means that, as long as we rule out other possible sources of injury from use of a straight-handled rake, we can properly conclude that "straight-handled rakes are better than the new rakes for minimizing risk of spinal injury." This is what answer choice (A) does, thereby strengthening the conclusion in the stimulus. Hope that helps.

@mehran I am also confused by this. I thought since the stimulus mentions injury from both pushing and pulling that it is saying both are a possibility?? I eliminated the correct answer because I thought that meant it was possible to get an injury from pulling.

@mehran I don't see how the correct answer choice -- "Compression stress resulting from pushing is the only cause of injuries to the spine that occur as a result of raking" -- is sufficient to guarantee the conclusion, that "straight-handled rakes are better than the new rakes for minimizing risk of spinal injury". If it's a super premise, shouldn't it be able to guaranty the conclusion without the support of any other premises? It seems like, in order to get to this conclusion, you have to the use other premises in the passage, in addition to the premise provided in the correct answer choice.

Hi, yes, you need to use the other premises. Arguments generally have more than one premise. We are looking for the thing that, if added, would make the argument correct. It does not need to be able to guarantee the conclusion on its own, it needs to fix the argument.