The question is NOT ' What is the main conclusion?', BUT 'What expresses the main conclusion?'.
So let us look for the main conclusion in the PARA.

It is a given that to be an intriguing person, one must be able to inspire the perpetual curiosity of others. Constantly broadening one's abilities and extending one's intellectual reach will enable one to inspire that curiosity. For such a perpetual expansion of one's mind makes it impossible to be fully comprehended, making one a constant mystery to others.
It is a given that to be an intriguing person, one must be able to inspire the perpetual curiosity of others. -- This sounds like a Premise
Constantly broadening one's abilities and extending one's intellectual reach will enable one to inspire that curiosity. -- Yes, this is a conclusion.
For such a perpetual expansion of one's mind makes it impossible to be fully comprehended, making one a constant mystery to others.---Use of FOR tells us it is supporting the conclusion.

Now, when we know the conclusion, let us see the choice that expresses this albeit in different words.

Constantly broadening one's abilities and extending one's intellectual reach => enables one to inspire that curiosity.

This is expressing the premise in a bit different wording.


This represents X=>Y, in other words as If X, then Y.
Fits our bill, but let us see other choices


Reorganizes the Support in different words


This choice too uses all the terms of conclusion, but 'If X then Y' to 'X is must for Y'. The conclusion says that Constantly broadening one's abilities and extending one's intellectual reach => enables one to inspire that curiosity. But, this does not mean Curiosity can be inspired ONLY through constantly.....


X => Y . Here Y is changed from the original meaning

B
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It seems that issue is whether B or D is the correct answer.
If we diagram the conclusion we get this :
Constantly broadening one's abilities and extending one's intellectual reach ------> one to inspire that curiosity.

If we diagram D we get this : To inspire the perpetual curiosity of others----------> one must constantly broaden one's abilities and extend one's intellectual reach.This is what we call a mistaken reversal in conditional reasoning. Since main point question types are like must be true question types ,the only form of comditonal reasoning that is accepted is the contrapositive or the repeat form.

diagramming B gives us : If one constantly broadens one's abilities and extends one's intellectual reach-------->one will be able to inspire the perpetual curiosity of others
This is the repeat form and is thus true