The correct option is D sluggish
Impetuous means acting or done quickly and without thought or care.The opposite of impetuous is sluggish, or slow to respond or make progress. Hence, Option D is correct. Among the rest of the options, poised means having a composed and self-assured manner, rash means acting or done without careful consideration of the possible consequences, gentle means having or showing a mild, kind, or tender temperament or character. These options do not express this antonym, hence incorrect.