Option C is incorrect under the HCIA-Cloud Service V3.5 networking model . Huawei Cloud's V3.5-era VPC documentation differentiates the two access-control mechanisms by their scope and rule behavior: security groups protect cloud server instances and use allow rules, whereas network ACLs protect subnets and support both allow and deny rules . Therefore, the statement that both mechanisms support both rule actions is inconsistent with the curriculum version used by this examination.

Option A is correct because a network ACL is associated with one or more subnets and controls traffic entering or leaving those subnets. Option D is also correct because security groups provide instance-level access control for resources such as ECSs. Huawei describes a security group as a collection of traffic-control rules applied to instances sharing common security requirements.

Option B is technically correct because these mechanisms can be layered. A security group provides access control around ECS instances, while a network ACL adds another security-control boundary around the subnet. Huawei specifically recommends using them together where comprehensive or fine-grained network protection is required.

Reference topics: Security Groups; Network ACLs; VPC Access Control; Defense-in-Depth.

===============