The author uses the idiom "pie in the sky" to describe Molly's unrealistic expectations about college. This phrase indicates an overly optimistic view that may not reflect reality. Therefore, the correct answer is B. idiom.
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The author uses the term 'pie in the sky' to illustrate Molly's unrealistic beliefs about college, making this an example of an idiom. An idiom conveys meaning that goes beyond the literal interpretation of the individual words. In contrast to metaphors and similes, idioms have a recognized meaning within a culture. ;