The '-sn' option in Nmap is used to perform a host discovery, which simply pings the hosts without actually scanning any ports. This is the correct answer as it minimizes the amount of traffic and reduces the chance of causing network disruption. The '-sV' option executes a service version detection, which is more intrusive and creates more traffic, going beyond the requirement of just discovering live hosts. The '-A' option enables OS detection, version detection, script scanning, and traceroute, which would not only produce more traffic but also try to scan and fingerprint hosts, which is not needed in this scenario. The '-p' option specifies the target ports to scan, which does not directly relate to host discovery without port scanning.