The argument states that reaching full output within a year is required for success: that is a necessary condition. From the fact that the firm is on track to meet that condition, the argument concludes that success is assured. But a necessary condition is not automatically sufficient. Meeting it removes one obstacle, yet it does not guarantee the outcome, since other things could still derail the plan.
(A) names this necessary-treated-as-sufficient slip, so (A) is correct. Each other choice names a real flaw type that this argument does not commit. (B) describes hasty generalization, but the conclusion is only about this one firm's plan. (C) describes false analogy, but the argument explicitly separates the firm's situation from the rivals' rather than treating them as alike. (D) describes an attack on the rivals themselves, but the argument only reports the neutral fact that their plans failed; it never criticizes them personally. (E) describes a key term shifting meaning between premises and conclusion, but both "success" and "full output within a year" keep one stable meaning throughout. Only (A) matches the flaw the argument actually contains.