Billy bought pencils and put them in his what?
Options:
- classroom
- kitchen sink
- backpack
- cabinet
- store
Step-by-step reasoning process below:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Pencils are usually used in a classroom. A pencil is a personal belonging. Students generally bring their backpacks to classrooms. Students usually keep their personal belongings in the backpack. The answer: backpack.