The correct selection is A. The failure results from managed-package Apex being non-certified during testing. The subscriber org must explicitly allow metadata deployment from a non-certified Apex package version; this is an org-level security preference, not a custom metadata setting and not a reason to replace the solution with Tooling API. From a deployment perspective, the same release should be reproducible across environments, with dependencies, metadata/data differences, API behavior, and target-org constraints identified before production. Automation is valuable because it turns deployment knowledge into a controlled process rather than relying on memory or manual reconstruction. The other choices either rely on manual reconstruction, use a deployment mechanism designed for a different scope, or fail to preserve dependencies and repeatability across target environments. For this scenario, the decisive point is therefore the platform behavior represented by the selected option (A. Apex Settings to allow the access to metadata is not switched on.). Applying that rule consistently keeps the implementation aligned with Salesforce-supported lifecycle practices and makes the resulting change easier to review, validate, and operate across environments.

Study Guide reference: Deploying — Metadata API and Tooling API; deployment validation; package/change-set deployment; data migration; dependency management.