(A) television, but the old style of door-to-door campaigning still has value because it allows– Looks good. The old style of door to door campaign should use Present perfect and we need the contrast.
(B) television, but the old style of door-to-door campaigning still would have value because of it allowing -still would have is incorrect.
(C) television; however, there is still value in the old style of door-to-door campaigning by allowing – “;” is not required. The rest of the sentence
...
(B) television, but the old style of door-to-door campaigning still would have value because of it allowing -still would have is incorrect.
(C) television; however, there is still value in the old style of door-to-door campaigning by allowing – “;” is not required. The rest of the sentence
...
