B. Whether or not Taiwan develops a closer relationship with mainland China or preserves the status quo affecting the United States
[
Grammatically incorrect. There is no conjugated verb in the main clause so the resulting statement is a fragment. Also,
whether or not is considered stylistically redundant.]
C. Whether or not Taiwan develops a closer relationship with mainland China or the status quo is preserved, it will affect the United States.
[
Grammatically incorrect. There is a parallelism error.
develops a closer relationship and
status quo is preserved are not parallel and they should be]
D. It affects the United States whether Taiwan will develop a closer relationship with mainland China or preserves the status quo.
[Grammatically incorrect. Again, the two parts of
or are not parallel, they are in different parts of speech].
D. It affects the United States whether or not Taiwan will develop a closer relationship with mainland China or preserve the status quo
[Again the same error. Using
It in the first part of the sentence is correct.]
So, the answer is A