The correct option is The cloud operator refuses to grant auditors the necessary access to examine the underlying infrastructure.

This is the common barrier because cloud providers control the physical hosts and hypervisor layer and they normally do not allow external auditors to inspect that level of the stack. Independent certification often requires direct access to host configurations, low level logs, and hardware artifacts and the provider's contractual and security constraints usually prevent that kind of access. In practice developers and auditors rely on the cloud provider's own third party attestations and reports when direct inspection is not possible.

The cost to commission an independent audit for a cloud hosted application is significantly higher than auditing a private data center is incorrect because audit cost alone is not the typical blocking factor. Many audits can be performed remotely and providers publish compliance evidence that reduces the need for costly direct inspection.

Most compliance standards require applications to run in company owned physical data centers to be eligible for certification is incorrect because most modern standards allow cloud deployments when appropriate controls are in place. Cloud providers frequently hold certifications such as SOC and ISO that enable their customers to achieve compliance.

Gathering forensic and audit evidence in a multi tenant public cloud environment is more complex than in an isolated on premises data center is incorrect as an answer because complexity alone does not usually prevent certification. While evidence collection can be more complex in the cloud there are logging services, APIs, and provider attestations that auditors use to obtain the necessary evidence.

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