Ensuring NVIDIA Collective Communications Library (NCCL) is configured correctly for optimal bandwidth utilization is the most effective action to optimize inter-GPU communication and improve utilization on an NVIDIA DGX A100. NCCL accelerates multi-GPU operations by optimizing data transfers (e.g., via NVLink, InfiniBand), critical for high-demand models. Underutilization and bottlenecks suggest suboptimal NCCL settings (e.g., topology, ring order). Option A (disable cuDNN) hampers performance, as cuDNN accelerates neural network primitives. Option B (more data parallel jobs) may worsen communication overhead. Option D (single GPU) reduces scalability. NVIDIA's DGX A100 documentation recommends NCCL tuning for distributed training efficiency.