You have been tasked with optimizing a legacy monolithic application running on a VM for cost. The application experiences variable traffic and is essential only during office hours. What should you do to optimize costs without refactoring the application?

*Explanation:* Implement a custom script to start and stop the VM based on schedules. A. Incorrect, App Engine Standard requires refactoring the application. B. Incorrect, Committed Use Discounts won't help in variable traffic scenarios and may add unnecessary costs. C. Correct, a custom script to start and stop the VM based on office hours will optimize costs. D) Incorrect, Preemptible VMs are not reliable for essential services. E) Incorrect, Cloud Functions would require refactoring the application.