For this answer choice to be sufficient (i.e. correct), we would need a direct relation between: 

X: ‘using scientific methods to examine the raised questions’ – what we’re told about parapsychology in the passage

and

Y: ‘conclusively answering the raised questions’ – what this answer choice introduces

i.e., if every field that does X also does Y, then parapsychology would be genuine science.

Basically,

1. Parapsychology does X. (passage)
2. If a field does X, then it does Y. (missing link – not actually given)
3. If a field does Y, then it is genuine science. (Option A)
4. Parapsychology is a genuine science (what we need to infer).

If we had all this information, including the second point, then we could say with certainty that parapsychology is a genuine science. However, we actually don’t have that link from the second point.

It is entirely possible that:

1. a field does X but doesn’t do Y (i.e. a field uses scientific methods to examine the questions it raises but doesn’t conclusively answer the questions)
2. a field does Y without doing X (i.e. a field conclusively answers the questions it raises without using scientific methods to examine them)

So, we don’t have a link between “using scientific methods to examine the raised questions” (which is our concern) and “conclusively answering the raised questions” (which is what the option talks about). So, the option has no impact on the argument, and is irrelevant.

Let’s add this statement to the argument. 

1. Parapsychology uses scientific methods to examine the questions it raises (basis).
2. Since parapsychology uses scientific methods, it will produce credible results (Option B).
   
3. Therefore parapsychology is a genuine science (main point).

Based on statements 1 and 2, can we infer statement 3?

This answer choice tells us about a result of parapsychology using scientific methods – credible results. We’re not concerned with whether parapsychology produces credible results. We can’t say that anything that produces credible results is a genuine scientific enterprise.

Irrelevant.

Let me first take an example to try to explain why this answer choice is incorrect.

Argument: John is taller than 6’. Therefore, John plays basketball.

Statement: Anyone who is shorter than 6’ does not play basketball. 

Question: Can the conclusion above be properly drawn if this statement is assumed?

It can’t. 

People shorter than 6’ not playing basketball does not prove for sure that those who are taller than 6’ play basketball. 

So, no, even if this statement is assumed, the conclusion that John plays basketball still can’t be properly drawn.

Similarly, even in the given context, if we add answer choice C to the argument:

1. Parapsychology uses scientific methods to examine the questions it raises (basis).
2. Any enterprise that does not use controlled experiments and statistical tests is not genuine science. (Option C).
   
3. Therefore parapsychology is a genuine science (main point).

The conclusion still does not follow with certainty. Even if all the enterprises that    don’t use controlled experiments and statistical tests are not genuine science, I can’t be certain that those that do use these methods are genuine science. 

(Say, people who don’t study don’t get good marks.

Does that mean that everyone who studies gets good marks?

Not necessarily, right?)

Moreover, the two methods: controlled experiments and statistical tests are merely examples of scientific methods. Fields could use scientific methods other than these two as well.

.

Let’s add this statement to the argument:

1. Parapsychology uses scientific methods to examine the questions it raises (basis).
2. Any field of study that employs scientific methods is a genuine scientific enterprise (Option D).
   
3. Therefore parapsychology is a genuine science (main point).

Based on statements 1 and 2, can we infer statement 3?

Once we add this answer choice to the argument, the conclusion follows for sure.

Given that (1a) parapsychology uses scientific methods, and (2) that any study that uses scientific methods is genuine science, parapsychology would certainly be genuine science.

Even if we add this statement to the argument, the conclusion can still not be properly drawn.

Remember, our objective is to be able to properly conclude that parapsychology is a genuine science. Whether the questions raised by parapsychology can be tested in controlled experiments does not get me any closer to making that conclusion.

Irrelevant.

Additional Notes

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1. Is option D an assumption required for the argument?
   
   It is not.
   
   [Caution: I hope my explanation below is clear, but it is possible that you find this point confusing. You may choose to skip this point. Or, if you have any follow up questions, feel free to ask 🙂 ]
   
   A necessary assumption would have been:
   Any field of study that employs scientific methods to examine the questions it raises is a genuine scientific enterprise.
   That is an assumption the argument is based on.
   
   Answer choice D supports the argument. However, it is not necessary for the argument.
   
   Let us understand this by negating the answer choice.
   Negation of option D: Some fields of study that employ scientific methods are not genuine scientific enterprises.
   
   First, I’ll divide fields of study that employ scientific methods into two categories. There could be fields of study that employ scientific methods to 
   a. examine the questions they raise 
   b. do something else
   
   So, even if some fields of the superset (fields that employ scientific methods) are not genuine science, the fields in the specific subset (fields that employ scientific methods to examine the questions they raise) could all still be genuine science. The argument doesn’t break down on negating answer choice D. So, that answer choice is not an assumption on which the argument depends.

2. Many students read the word “assumed” in the question stem and assume that it is a typical assumption question. Remember, precise reading is required at every step, including while understanding the question stem. 

3. If the question stem fits into a category/ concept you have learned, fine. But if it doesn’t, that’s fine too.  End of the day, our objective with every CR question is to answer the question that’s been asked. To force-fit a question into a category is a mistake.

4. 
a. If there is an answer choice in such a question that is an assumption that the argument depends on, but it is not sufficient to lead to the conclusion, the answer choice would be incorrect.

b. If there is an answer choice that is not an assumption required in the argument, but it is sufficient to lead to the conclusion, the answer choice would be correct. That’s the case with the correct answer in this question.

5. . Another official question that asks us to choose a ‘sufficient statement’:
https://gmatclub.com/forum/biologist-species-with-broad-geographic-ranges-probably-tend-to-endur-306112.html