What causes Gulliver to fall asleep after being treated by the Lilliputians?

The correct choice indicates that Gulliver falls asleep due to a sleepy potion added to his wine. Within the context of the story, the Lilliputians, who are much smaller than Gulliver, use this potion as a means of subduing him after he is captured. This choice emphasizes the cleverness and resourcefulness of the Lilliputian people in managing a giant like Gulliver, as they need to ensure he remains compliant while they decide on how to handle him.

The use of a potion reflects the themes of power dynamics and the manipulation of strength, highlighting Gulliver's vulnerability in a situation where he is physically much larger yet rendered defenseless through the Lilliputians' ingenuity. This also serves to illustrate their culture and the lengths they will go to maintain control over an uncontrollable situation.

In the context of the other options, a lullaby would not be effective given the circumstances, soothing ointment generally refers to topical treatments rather than causing sleep, and a magical spell introduces an element of fantasy that is less aligned with the rational, satirical tone of the story. Thus, the sleepy potion in the wine fits perfectly with the narrative and the actions of the Lilliputians.