Which of the following is the BEST example of IaaS?

Hardware owned by the user but managed and hosted by a third party describes a co-location (colocation) arrangement, not IaaS, because the customer still owns the physical assets.

When hardware and software are both owned, hosted, and managed entirely by the third party, that describes the SaaS (Software as a Service) model, not IaaS.

In the IaaS model, the third-party provider owns, physically hosts, and fully manages the underlying infrastructure including servers, networking, and storage. The customer consumes this infrastructure on demand via virtualization and is responsible only for the operating system, middleware, and applications running on top of it.

Hardware owned and managed by the user but merely hosted by a third party describes a colocation or hosted infrastructure model where the customer retains physical ownership and management responsibility.