Sentence Correction

Under high pressure and intense heat, graphite, the most stable form of pure carbon,
changes into the substance commonly referred to as diamond and remaining this way
whether or not the heat and pressure are removed.
A. remaining this way whether or not
B. remaining like that even as
C. remaining as such whether or not
D. remains in this way although
E. remains thus even when
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Since parallelism is one of the issues here....i cud short list it to D and E...

But whats wrong with even WHEN ?? Is the that WHEN always refers to time ??
i Some how feel that the use of ALTHOUGH in option D is not appropriate.

Could anyone explain the problem ??

Thanks in advance!! :- )

although is used to introduce a statement that makes your main statement seem surprising or unlikely

Now I guess we have to find the best answer not the perfect answer.

breaking down to D and E is easy but I guess D seems more appealing than E ( the use of thus and even together which just does not sound right
) .

It has to be 'remains'. D is the best option by PoE then.

although shows contrast

in this sentence, we intend to say that carbon continues to remain in the form of diamond even without the said conditions.

Remains is the right verb for the sentence

D.remains in this way although; shows a state even without the conditions by use of although. remains is also followed by in this way which is correctly pointing to state of diamomnd
E. remains thus even when - Thus after remains, is odd and does.