Final answer:
A fire suppression system is an example of physical infrastructure hardening, as it involves equipment to prevent fire damage. Antivirus software, two-factor authentication, and hardware-based network firewalls are cybersecurity measures, not physical infrastructure hardening.
Step-by-step explanation:
Physical infrastructure hardening refers to the protective measures taken to make physical infrastructure more secure against various threats such as natural disasters, accidents, or attacks. Among the provided options, fire suppression systems are an example of physical infrastructure hardening. This is because it involves the installation and maintenance of equipment designed to detect and extinguish fires, thereby preventing damage to physical assets.
By contrast, antivirus software and two-factor authentication are examples of cybersecurity measures intended to protect information systems from malicious software and unauthorized access respectively. A hardware-based network firewall is also a cybersecurity measure that filters incoming and outgoing network traffic to protect against cyber attacks.