What would you need a light source to use?
Options:
- dard
- sky
- books
- candle
- house Let's think step by step:

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
Books are a written or printed work consisting of pages glued or sewn together along one side and bound in covers. We would need a light source to use books. So, the answer is books.