Most of the time, they were direct carry-overs from the five undoubtedly formative years he had spent as a regular panelist on "It’s a Wise Child," when, rather than seem to flaunt his somewhat preposterous ability to quote, instantaneously and, usually, verbatim, almost anything he had ever read, or even listened to, with genuine interest, he cultivated a habit of furrowing his brow and appearing to stall for time, the way the other children on the program did.
There are no more uses of "preposterous" in the book.
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They can’t be seriously considering such a preposterous idea.
a preposterous attempt to turn back the pages of history