The correct answer is C. pose.
The word "pose" means to present a problem or difficulty. In this case, the dissidents are presenting a problem for the political party. The other options are incorrect because they do not accurately reflect the meaning of the sentence.
The word "cause" means to bring about something, especially something bad or unfortunate. In this case, the dissidents are not bringing about the problem; they are simply presenting it.
The word "give" means to provide or hand over something. In this case, the dissidents are not providing the problem; they are simply presenting it.
The word "No improvement" is incorrect because the sentence is already grammatically correct and does not need to be improved.