A revolving door is convenient for two direction travel, but it also serves as a security measure at a what?
Options:
- bank
- library
- department store
- mall
- new york
Please answer and provide answer explanation.

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
Security measure is required at a bank. At a bank, a revolving door which serves security measure is convenient for two direction travel. The final answer: bank.