Critical thinking requires that a. conclusions be held constant after their initial determination b. conclusions be adjusted as necessary to incorporate new knowledge c. information from a particular source only be verified the first time the source is used d. there be a single solution to a particular problem

B. conclusions be adjusted as necessary to incorporate new knowledge
Critical thinking refers to the process of creating well thought, logical and sound judgments. It requires not only receiving and accepting arguments but verifying and testing the validity and truth in all the arguments presented. 

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The answer is B: Conclusions be adjusted as necessary to incorporate new knowledge.