This is a parallel reasoning question.
For this type of question, I try to go through the answer choices to see if they have matching premises and conclusions, first. After eliminating those that don't match, if there is still uncertainty, I try to make an abstract structure from the stimulus and apply it to those answer choices left.
First thing that I noticed from the stimulus is "unlikely" from the conclusion. This indicates a level of certainty: it is "probable", not definite.
Looking at conclusions from each answer choices, we should be able to eliminate A), D), and E).
A) is too definite with "clearly no reason", while D) and E) doesn't have the term for "probability" (don't get confused with "unlikely" in their premises).
Now we have B) and C). There are two things that distinguishes these two.
1) Looking at premises for these two and stimulus, I see all of them is quoting someone's advice. But C) has "often" in it while B) and the stimulus don't. This puts C) less of an answer choice.
2) Looking at the flow of the premises, stimulus gives us a general fact as the first premise which advice NOT to do a certain action. And then starting with “however”, the author introduces a second premise that provides an exceptional case to the first premise. And then the author goes on to conclude that what he/she introduced in the first premise would not "probably" follow.
While B) follows this structure perfectly, C)'s first premie introduces an advice FOR doing something and then its exceptional case is not related to the premise while the stimulus and B) do.
From these two, we can conclude that correct answer is B)
But just to make sure of it, let's make an abstract structure:
Advice AGAINST A (planting snap peas after late April) because of B (not develop well in warm weather).
However, because of C (unusually cool), A will “probably” result in ~B.
Now, let's see how B) and C)'s abstract structure matches with the stimulus.
B)
Advice against A (facing south) because B (not thrive in direct sunlight).
However, C (no direct sunlight due to evergreen trees’ shade), A will “probably” result in ~B
>> Match
C)
“often” advice FOR A(using impatiens) because B (impatiens does well in shade)
However, C (maple trees absorb all moisture — This is supposed to be related to B), A will probably ~B
>> Close but not quite the match.
So, this confirms B) to be the correct answer.