Which of the following features helps in balancing CPU resources among virtual machines?

DRS, or Distributed Resource Scheduler, is specifically designed to balance CPU and memory resources among virtual machines within a cluster. It actively monitors the resource usage of each VM and the overall resource availability in the cluster. When it detects that a VM is in need of additional resources or when resource contention occurs, DRS can automatically migrate virtual machines to other hosts in the cluster to ensure that resource distribution remains optimal. This helps maintain performance and efficiency across all VMs.

In contrast, vMotion primarily facilitates the live migration of VMs from one host to another without downtime, which supports maintenance operations and load balancing but does not actively manage resources like DRS. Network I/O Control is focused on managing network resource allocation among VMs, ensuring that bandwidth is distributed according to policy rather than balancing CPU resources. Storage DRS similarly deals with storage resource management, optimizing the placement of virtual disks but not directly impacting CPU resource allocation.

Thus, DRS is the feature specifically designed for managing and balancing CPU resources among VMs, making it the correct choice for this question.