Dear manpreet singh

I found this a relatively straightforward question. I'll share my reasoning.

In their native habit, amaryllis plants go dormant when the soil in which they are growing dries out during the dry season. Therefore, if amaryllis plants kept as houseplants are to thrive, water should be withheld from them during part of the year so that the plants go dormant.

Which one of the following is an assumption on which the argument depends?

The first sentence tells us factual information, including the fact that these plants go dormant in the dry season. It sounds as if the dry season might be a tough time. Maybe the dormancy just helps them get through the dry season.

Then, the second sentence is a recommendation --- in houses, where watering could be continuous throughout the year, the plant owners should artificially create a "dry season" to stimulate dormancy. OK, right away, that must mean dormancy is a good thing --- it has some beneficial purpose other than simply helping the plant to survive dry season.

That was my pre-thinking before looking at the answers, and it helped me to predict what turns out to be the OA, [spoiler](E)[/spoiler].

For clarity, here's an analysis of the other answer.
(A) Most kinds of plants go dormant at some time or other during the year.
Argument by analogy --- weak. Even if plans in the wild have to go dormant to weather harsh conditions, why would plant owners need to mimick these harsh conditions in the controlled environment of indoors? This is incorrect.
(B) Amaryllis are more difficult keep as houseplants than other kinds of plants are.
Irrelevant. How easy or difficult another plant is tells us zilch about the proper way to treat an amaryllis. This is incorrect.
(C) Water should be withheld from amaryllis plants kept as houseplants during the exact time of year that corresponds to the dry season in their native habitat.
A tempting distractor. The argument simply suggests that homeowners withhold water "during part of the year" --- apparently, the dormancy itself is important, but not exactly when it happens. This is incorrect.
(D) Any amaryllis plant that fails to thrive is likely to have been dormant for too short a time.
Another brilliant distractor. The argument says nothing about what would constitute "too much" or "too little" dormancy, and whether either imperils the plant. This is incorrect.
(E) Going dormant benefits amaryllis plants in their native habitat in some way other than simply preventing death during overly dry periods.
Exactly what I predicted when I read the prompt paragraph. If going dormant has no benefits other than helping the plant whether a rough dry season, then the plant owner, who would be able to water the plan 365 days in a year, would have absolutely no reason to deviate from the watering schedule to create an artificial drought.

OA = [spoiler](E)[/spoiler]

Here's a blog on GMAT CR assumptions.
https://magoosh.com/gmat/2012/arguments- ... -the-gmat/

Does all this make sense?
Mike