The correct option is D sluggish
The word 'agile' refers to being able to move quickly and easily.
Option A, brisk refers to being active and energetic.
Option B, emaciated refers to being abnormally thin or weak, especially due to some illness or lack of food.
Option C, feeble refers to lacking physical strength, especially as a result of age or illness.
Option D, sluggish refers to lacking energy or alertness.
Thus, according to the meaning, the word 'sluggish' is the opposite of the word 'agile'.