Although it was known that inductive action travelled with finite velo

first of all IMO there should be no comma before AND(WOULD BE HAPPY IF SOMEONES EXPLAINS THIS)
AS and is acting as parallelism marker.
SUBORDINATE clause starting with ALTHOUGH donot need a conjuction to connect clauses.
ALTHOUGH X ,Y==>this is correct construction===>1
ALTHOUGH X ,and Y===>THIS IS INCORRECT===>2
NOTE: X AND Y are clauses here.

in this case clause X is :it was known that inductive action travelled with finite velocity in space, [u]and that an electro-magnet would affect the space about it practically inversely as the square of the distance
CLAUSE Y : nearly all the physicists failed to form the only conception of it that was possible.


A. and that an electro-magnet would affect the space about it practically inversely as the square of the distance
this is correct as THAT is required for parallel structure

B. and an electro-magnet would affect the space about it practically inversely as the square of the distance
THIS ONE lacks THAT (which is required for parallelism)....moreover it seems to be type2 construction as explained above..which is incorrect

C. and also that an electro-magnet would affect the space about it practically inversely like the square of the distance
and also ==>redundant.....like =>incorrect it should be AS

D. and that an electro-magnet would affect the space about them practically inversely as the square of the distance
PRONOUN NUMBER ERROR . (IT is needed in place of THEM)

E. and also known that an electro-magnet would affect the space about it practically inversely as the square of the distance
AND ALSO ==>REDUNDANT
KNOWN==>NOT REQUIRED

HENCE OPTION A