Explanation:

In Azure networking, each Network Security Group (NSG) is created with a built-in set of default security rules. Microsoft's documentation for NSGs explains: "Azure creates several default security rules within each network security group. You can't remove the default security rules, but you can override them by creating rules with a higher priority." The rule processing model is priority-based: "Security rules are processed in priority order, with lower numbers processed before higher numbers. Once a rule matches traffic, processing stops." Because the defaults have relatively low precedence (high priority numbers), an administrator can create an explicit allow or deny rule with a lower priority number to supersede the default behavior.
This is why the correct completion is override rather than copy or delete. You cannot delete the default rules; they remain present to provide baseline behavior (such as denying inbound traffic from the internet by default and allowing virtual network traffic). Instead, you override the defaults by adding your own NSG rules- using lower priority numbers-to achieve the desired access control outcome while preserving Azure's baseline protections and evaluation logic.