Final answer:
At project closeout, the documentation that must contain the certification of flameproofing for finishes is Record documents for finish applications and furniture installations.
Step-by-step explanation:
At project closeout, the documentation that must contain the certification of flameproofing for finishes is C. Record documents for finish applications and furniture installations. These record documents should provide evidence that the finishes have been properly flameproofed. They may include information such as the type of flameproofing used, the date of application, and any necessary laboratory test results.