Thanks for the question! So take a look at what (D) tells us, that outside information cannot influence group decisions once they’ve been determined by groupthink. And recall that this passage is asking us for something that we can infer from the passage; this is basically a Must Be True question, and should be treated as such. We have to find strong support for this premise, and we should be wary of strongly worded premises. And this premise is strongly worded: is it true that outside information absolutely CANNOT at all influence group decisions once they’ve been determined by groupthink? No, the passage doesn’t go as far as to suggest that. The passage just says that one factor of groupthink is that groups may be “closed-minded to warnings of problems and to alternative viewpoints” (lines 47-48) and that the benefit of the doubt should be given to group consensus (lines 33-34). But nothing says that groups that have fallen to groupthink are absolutely impervious to any outside influence at all. So (D) is too strong to be properly inferred from the passage, and incorrect.
Hope this helps! Feel free to ask any other questions that you might have.