Answer:
In F. Scott Fitzgerald's novel "The Great Gatsby," Tom Buchanan senses that Gatsby is a bootlegger based on several clues.
Firstly, Gatsby is known for throwing extravagant parties that are attended by many people, including well-known gangsters and bootleggers. This leads Tom to suspect that Gatsby may be involved in illegal activities himself.
Secondly, Gatsby is extremely wealthy and has acquired his wealth seemingly overnight, which seems suspicious to Tom. Tom believes that it is unlikely that Gatsby could have earned such wealth through legitimate means.
Thirdly, when Gatsby invites Daisy and Tom to his mansion for tea, he serves them alcohol from his own stock, which is of suspicious quality. This also suggests to Tom that Gatsby is involved in bootlegging.
Overall, Tom's suspicions about Gatsby being a bootlegger are based on a combination of his reputation for throwing wild parties, his sudden and unexplained wealth, and the fact that he serves them questionable alcohol.