Important doubt

[nataashaj]

The cause of Osgood’s syndrome is unknown, nor is it known why the disease appears to be increasing in the United States.

(A) unknown, nor is it known
(B) unknown, neither do they know
(C) not known, nor do they know
(D) not known, unknown too is
(E) not known, neither do they know

[kc_raj]

IMHO A,

nor is coordinate conjunction joining two clauses,

[riteshbindal]

I also think it is A.
There is no referent for "there" so B, C and E can be removed.
D makes it awkward by saying "unknown too is". So the best option left should be A.

OA plz

[nataashaj]

correct answer c

[nataashaj]

sorry sorry its A

[riteshbindal]

sorry sorry its A

Thanks for the correction