“She dips a corner of her sleeve / like a brush into water”
A simile is a comparison between two unlike things using like or as. Only the first and the last options contain the word like or as. The first option is incorrect because it is not making a comparison. It is merely stating that her legs are under her while she sits on a pillow. The last option is a simile because it uses the word "like". It compares a sleeve dipped in water to a brush dipped into water.
