Ravi..
frankly this is one of the most common traps gmat sets for its takers. so every time you see something like this, think about it and ensure u dont fall for it
the passage states an intertextual means DEFINATELY written in response to some one else's literature. but non intertextual DOES NOT NECESSARILY mean that there could be no relationships with other works.
Thats where C falters... it says
if inter textual -- > works are related ( one is written in response to another)
if not ---> The works are not related.
here is an example.
lets say u designed a concept 2+2 =4
if i say 2+2 is not 4 but 2+2 = 5 then thats intertextual
but if i state a new theory that 2+2 + 4 = 4+ 4 = 8
i am not creating a work in response to yours (im not conflicting your statements) but at the same time i am using SOME of your concepts.. some of celly's concepts maybe, some my own and then im creating a new one altogether.
so C misses out on this kind of possibility
D echoes the last sentence in the CR nicely. hope this helps.