What command would you use to display statistics on items such as round-trip times?

The command used to display statistics on items such as round-trip times is ping. This utility is primarily used to test the reachability of a host on an Internet Protocol (IP) network and measure the time it takes for packets to travel from the host to the destination and back. When you use ping, it sends out Internet Control Message Protocol (ICMP) Echo Request messages to the specified address and listens for Echo Reply messages in return. The output provides useful statistics, including the round-trip time for each packet, which is crucial for diagnosing network performance issues.

While other options like iperf and mtr also provide valuable information related to network performance, they serve different specific purposes. Iperf is primarily used for measuring bandwidth and testing the maximum TCP and UDP bandwidth, rather than round-trip times. Mtr combines the functionality of ping and traceroute, showing the route packets take and the latency to each hop along the way, but it focuses on the path rather than just display round-trip times for a single destination. Iftop is specialized for monitoring bandwidth usage on network interfaces but does not provide round-trip time statistics.

Thus, ping is clearly the most appropriate choice for directly displaying statistics related to round-trip times.