(A) does have two sufficient conditions (existing structure and planned development) leading to the same necessary condition (on the map). However, this argument's flaw is that it fails to recognize that a sufficient condition has been triggered: the development in (A) is an existing structure, so will be on the map.

To match the flaw from the stimulus, (A) would need to identify a structure that will be on the map, and then arbitrarily conclude that it is either an existing structure or a planned development. That would be the right combination of sufficient-necessary confusion and arbitrary choice.

(B) doesn't have two sufficient conditions leading to the same necessary condition, which diverges from the stimulus' structure. Instead, (B) fails to consider that a condition which was once sufficient to establish something is a public building (a blue dot) may no longer be sufficient, since public buildings are now marked differently.

A better version of (B) would say that both blue and purple dots marked public buildings. It would then identify a public building, and arbitrarily conclude that it would be marked by either a blue or purple dot. That would match the stimulus.

There's no flaw in (C). Given that the legend says that thoroughfares are marked by solid lines rather than dotted, it’s logical to conclude that the mapmakers made a mistake by marking a thoroughfare with a dotted line.

(D) doesn't commit sufficient-necessary confusion, which it would need to match the stimulus. Instead, (D) establishes two items that share a common characteristic—being marked with a solid line—and assumes that there’s no other way of determining which item a particular solid line represents.

(E) presents two sufficient conditions leading to the same necessary condition: both monuments and hospitals are marked with purple dots. (E) also arbitrarily concludes that an item meeting the necessary condition must meet one of the sufficient conditions: a purple dot is taken to mean a hospital, without any reason to think it's not a monument—or another building. (E) matches both elements of the flaw in the stimulus.