On Weaken questions you are sometimes looking for a shift in the author's words. The original argument discusses the rise in unemployment and Z responds with wording discussing the level of unemployment. This shift in language opens up an opportunity for assumptions - assuming that both words are the same.
Thus D shows the assumption between the level of unemployment and the rise in unemployment and therefore weakens the article.
Thus D shows the assumption between the level of unemployment and the rise in unemployment and therefore weakens the article.