Of the listed options, only inbound traffic flow inspection can directly protect against zero-day attacks. Here's why the other options are less effective: * Outbound: This inspects traffic leaving the network, which wouldn't necessarily catch malicious code entering from outside. * North-south: This refers to traffic between the internet and the internal network, which includes both inbound and outbound traffic. While inbound traffic is part of north-south flow, it's not the only component. * Internal: This inspects traffic within the internal network, useful for malware detection but not specifically zero-day attacks at the entry point. * East-west: Similar to internal traffic, this focuses on communication between devices within the network, not necessarily catching external threats. Therefore, the most relevant option for zero-day protection is "C": Inbound By inspecting inbound traffic, firewalls can potentially identify and block suspicious activity even if it exploits an unknown vulnerability (zero-day).