Explanation

An overview of the passage suggests that the first sentence is relatively self-contained and that the blank is answerable without the succeeding sentences, where the topic shifts slightly. The colon after the first blank signals that what follows will define the word in the blank and will explain what danger Mill was concerned about. It says that without challenge, one’s opinions grow “weak and flabby” and therefore one becomes complacent, not tendentious or fractious. A quick reading of the next two sentences suggests that the topic will be another danger that Mill described, “the danger of partiality and incompleteness.” Free and open discussion needs to take place because each person’s opinion tends to “embrace only a portion of the truth” and others’ views are partially right, or never completely “erroneous.” The other choices for the second and third blanks deal with change, immediacy, or antithesis, none of which relate to the
second danger of “partiality” or “incompleteness.”
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