Stream of consciousness rationale: Ketchup is used on foods, not in the bath-tub.
The question and answer pair are described below.
Q: One of the following sentences is nonsensical. Which one is it?
Options:
- Sentence A: "You must fill up a bath-tub with water to take a bath."
- Sentence B: "You must fill up a bath-tub with ketchup to take a bath."

A: Sentence B