An enterprise wants to provide low-cost delivery of network systems that can be scaled on...

A (IaaS within a private cloud):IaaS allows on-demand scaling of compute and storage resources, and private cloud deployment reduces capital expenditures by pooling hardware resources and increasing utilization, while allowing control over security and compliance.

Other options explained:

B: On-prem IaaS still requires significant CapEx.

C: PaaS delivers platform services, but the scenario is focused on network systems.

D: SaaS on-prem is uncommon and does not address infrastructure scaling.