Which field in a Pod spec defines resource requests and limits?

Correct answer: resources

Option C, resources, is correct because in a Kubernetes Pod spec the container's resource configuration is nested under the `resources` field, which contains both the `requests` sub-field (guaranteed minimums used by the scheduler) and the `limits` sub-field (enforced maximums enforced by the kubelet). Option A, limits, is a sub-field inside `resources`, not the top-level field that contains both requests and limits together. Option B, constraints, is not a valid field in a Kubernetes Pod or container spec. Option D, requests, is likewise only a sub-field inside `resources` and cannot stand alone as the top-level field that encompasses both requests and limits.