What if those areas placed with yellow tape become more eroded than before? Answer E doesn't explain how the yellow tape works to stop further erosion.
First off, here's a link to what is meant by yellow tape: Yellow Tape Picture. Hopefully that will help provide you with some better visual context for what's happening here. Now here's the text again:
Hightrail Park, a state park popular amongst weekend hikers, is suffering erosion along its trails. The primary cause are the many hikers, who looking for a quicker route between the switchbacks, cut between trails, thereby trampling undergrowth. Without grass and weeds, the land abutting the trails is more prone to erosion. To combat this problem, state park officials have placed yellow tape on those parts of the trail where erosion is most significant. State park officials expect that the park will not witness any erosion more extreme than what the park is currently witnessing.
I've highlighted the end because it's helpful for answering the question. Let's break it down a bit:
Action: Yellow tape around areas with most erosion
Goal: Prevent erosion from becoming more extreme
It's important to note that the goal is not to prevent all erosion, just to keep the rate of erosion from becoming worse. Now we want to find something that supports this. Basically we want to know which answer the park officials are assuming to be true in order for their plan to work. How exactly the yellow tape would function isn't really important to this question. We're just trying to find the assumption made by the park officials.
And now we can look at our answer choices and understand the explanation a bit better:
(A) Hikers who hike between trails tend to hike along a similar route, thereby making erosion more likely in certain areas along the trail. This only says that erosion is more likely to occur along certain parts of the trails. But we already know this. That’s why these eroded parts are going to be covered up with tape.
(B) Hikers who hike during the week are not as likely to walk on the land between the switchbacks. Even if weekday hikers are better behaved, this fact doesn’t relate to the plan to stop the erosion and the prediction of the effect of this plan.
(C) Erosion in the state park can be caused by others factors such as significant rainfall. This answer is very tempting. It, however, weakens the prompt. It is not an assumption the argument makes. Had (C) been, “the only causes of erosion along the trail is that caused by hikers trampling growth underfoot”, then we would have had a winner.
(D) The yellow tape at higher altitudes along the trail, where weather is more severe, will fall apart at the same rate as the yellow tape located at lower altitudes. This is tricky because it relates to the yellow tape. But what is (D) actually saying? That all of the tape is going to fall apart at the same time. But what if the tape at higher altitudes really falls apart faster? Will that mean that parts of the trail at higher elevations are going to be more eroded? Can we even assume that the tape is going to decay to the point that it no longer serves its purpose? All (D) says is the tape is going to break down faster; we don’t know to what extent it will actually break.
Answer choices like (D) are very tricky. Essentially, this kind of answer is asking you to go away from the text and ask, "What if X?" or "What if Y?" Then you get wrapped up in a tangential idea that isn't supported. Be careful about this as it happens in the harder RC questions.