We are given information that the plant X cannot survive in the desert, however it can survive in the surrounding areas. The question asks to resolve the paradox.
Pre-thinking - The premise provides information regarding the conditions in which the plant Y thrives and provides details on the climate in the dessert. The climate in the desert does seem a bit extreme
"Desert X is an environment with constant, powerful sunlight, and almost no moisture".
We have to resolve the paradox as to why the plant survives in the neighboring regions but not in the dessert.
1) What if the dessert soil is not suitable.
2) What if there are predicators in the dessert but not in the surrounding areas.
3) What if the temperature in the dessert is too harsh for the plant to survive.
Answer Choice Elimination -
In the light of above pre-thinking, let's perform answer choice elimination.
(A) Desert X’s climate is far too harsh for the animals that normally feed on Plant Y.If there are no predicators in the desert, the plant should thrive. However, we are told that the plant doesn't thrive in the dessert.
(B) For one week in the fall, Desert X gets consistent rainfall.This seem an interesting option, as we are told that the plant requires very little moisture. However, the passage also tells us that the plant Y does it survive long when introduced in the dessert. If the rainfall is the cause for the plant not thriving in the dessert, the plant should survive the 51 weeks when there is no rainfall. We can park this option and return if we don't find a better one.
(C) The environment around Desert X is ideally suited to the needs of Plant Y.Doesn't resolve the paradox as no new information is provided in this option. From the passage we know that the plant Y thrives in the neighboring regions, hence the environment must be suited for the growth.
(D) Due to the lack of sufficient moisture, Desert X can support very little plant life.Note the word 'sufficient moisture'. The option provides a general statement that the dessert can support very little plant life due to lack of sufficient moisture. We are not sure if the moisture in the desert is sufficient for the growth of plant Y. Also, the premise states that the plant Y requires very little moisture to thrive, so all the more this options doesn't provide any information to resolve the ambiguity.
(E) Plant Y cannot survive in temperatures as high as those normally found in Desert X.This option is way better than B. The option provides a reason in line with our pre-thinking. As the temperatures in the desert is extreme (something that the premise also tells us), the plant cannot thrive in dessert. Its for the same reason the plant does it survive long when introduced there.
IMO - E