The stimulus tells us about two groups of very long, footpath-like lines found in the Peruvian desert. The first group of lines is shaped like a sunburst, with many straight lines branching out from the same point. The second group of lines is curved and forms a large bird shape. The two groups cross over each other. This phenomenon is the context we're given.

The argument we're concerned with is made by an investigator, who hypothesizes that the lines were used for aliens to land their spaceships. In support, the investigator explains that the lines wouldn't have been useful as roads: they're too closely-spaced, they end at random places, and a sunburst shape wouldn't make sense for roads.

The investigator doesn't support the hypothesis that the lines were alien landing strips with direct evidence. Instead, the investigator eliminates another possible explanation by showing that its implications wouldn't make sense. To do so, the investigator has to assume that these are the only possible explanations, because otherwise eliminating one wouldn't show the truth of the other.

The correct answer might describe both these elements of the argument, or only one. It also might be phrased in abstract language that's hard to recognize. To avoid overlooking the correct answer, we want to tie the answer choices back to the stimulus so we can verify whether they actually describe the argument.