Why is D incorrect?

Hi @kenken, Happy to help! (D) is incorrect because it makes a generalization about all industries i.e. that some cooperation among manufacturers in the same industry is beneficial regardless of what industry they work in. The passage directly contradicts this, stating that many machines are "perfectly useful in isolation from others." Therefore, cooperation would be neither necessarily nor beneficial in these industries. Hope this is helpful! Please let us know if you have any further questions.