Final answer:
The best secondary verification control for physical presence in an unstaffed computing facility, along with motion detectors, would be a mantrap, which allows controlled access through a sequence of doors.
Step-by-step explanation:
Rajat is considering security measures for a new computing facility that will not be regularly staffed. He aims to implement motion detectors, but seeks a secondary method for verifying physical presence. Among the choices given, the best option for secondary verification would be mantrap. Mantraps are security devices that control access to a secure area through a small space with two or more doors. The idea is that only one door can be opened at a time, allowing security personnel to vet individuals or confirm their authorization before they enter the secure area. CCTV (closed-circuit television) could serve as an additional verification measure by providing visual confirmation of individuals detected by the motion sensors, but a mantrap ensures a physical, confined checkpoint.