Piyushggmat
What is this parallel structure people are talking about in this question.?? Noun to Noun Parallelism.
This is more about logic than parallelism. After all, I can write, "Tim is tall," even though "Tim" is a noun and "tall" is an adjective, right?
So we want to ask ourselves: which of these constructions makes sense?
1) One legacy... is the realization that
2) One legacy... is to realize
3) One legacy... is realizing
A legacy, or lasting consequence, can certainly be a
realization that something will happen. So the first example seems fine.
But the other two don't really make sense. In both cases, it kind of sounds as though the legacy is itself having a realization. Not terribly logical. So that kills (C), (D), and (E).
And then (A) has a clear pronoun-referent error, using the plural "their" to refer to the singular "a person."
That leaves us with (B). No parallelism required here.
I hope that helps!