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!! :- )