I understand why B isn't correct. But E does not seem correct either. We can see this from the negation test. If E is negated: "A factor harmful to some older local industries in a region MUST discourage other businesses from relocating to that region." Businesses can be discouraged by Factor A from relocating to a region but encouraged by Factor B. In such a scenario, the truth of the claim would depend on which factor was stronger. So I would say that the argument does not depend on E.