How does Gulliver obtain his boat?

Gulliver obtains his boat after it washes ashore, which means he finds it in the sea. This event is significant within the context of the story, as it highlights Gulliver's resourcefulness and the element of chance that often accompanies his travels. He is shipwrecked and separated from his crew, and it is through a fortuitous discovery that he is able to continue his journey. This points to a broader theme in "Gulliver's Travels," where chance and circumstance heavily influence Gulliver's adventures.

The other options do not align with the narrative. For instance, Gulliver does not build the boat himself, nor does he receive it from a merchant. There is also no instance in the text where he trades with the Lilliputians for a boat. This discovery is central to Gulliver's journey, setting the stage for his subsequent encounters in Lilliput.