Explanation

Because the second half of the sentence illustrates the idea that “structure mirrors thought,” any word that fills the blank must be similar in meaning to “convoluted.” The two words that are similar to “convoluted” are “complicated” and “involved” (Choices A and F), which produce sentences alike in meaning. “Fanciful,” while somewhat similar in meaning to “convoluted,” is not as similar to either “complicated” or “involved” as those words are to each other. The other answer choices are not similar in meaning to “convoluted,” and thus do not produce coherent sentences.
Thus the correct answer is complicated (Choice A) and involved (Choice F).
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