Security groups are stateful, and network access control lists $($ACLs$)$ are stateless. What is the difference between stateful and stateless?

Stateful means that return traffic is automatically allowed. Stateless means that return traffic must be explicitly allowed by rules.

Stateful means that return traffic must be explicitly allowed by rules. Stateless means that return traffic is automatically allowed.

Stateful means that return traffic must be explicitly allowed by rules. Stateless means that return traffic is never allowed.

Stateful means that return traffic is never allowed. Stateless means that return traffic must be explicitly allowed by rules.