Spot the error. His eyes gained sparkle; his mind, which was adequate if not brilliantly equipped, began to move more adventurously.

Explanation

The correct answer is Option D: "more adventurously." Although it is used correctly as an adverb to describe how his mind began to move, the phrase should be in the past tense, thus it would be better phrased as "moved more adventurously."Option A, "sparkle," is not an error as it correctly describes the brightness in his eyes. Option B, "adequate," is also used correctly to describe the sufficiency of his mind. Finally, Option C, "brilliantly," while an adverb that is correctly placed, suggests a degree of excellence that is outside the context of the sentence. Therefore, the only error is in the use of "more adventurously" in its current form.