Which computers can communicate directly without any routers involved?

The ability for two computers to communicate directly without any routers is primarily determined by whether they belong to the same subnetwork (or subnet). This is determined by their IP addresses and subnet masks.

In the scenario given, the correct answer is the pair of addresses 10.5.5.1/24 and 10.5.5.100/25.

To understand this, first consider what the subnet mask means in relation to the IP address. For the first address, 10.5.5.1/24 means that the first 24 bits of the address are used for the network part, leaving the remaining 8 bits for hosts. Therefore, the network is 10.5.5.0, and it can accommodate hosts from 10.5.5.1 to 10.5.5.254.

Next, the address 10.5.5.100/25 indicates a subnet mask that allows for a network range of 10.5.5.0 to 10.5.5.127. Since both addresses share the same first 24 bits (10.5.5), they fall within the same overall network, which is also supported by 10.5.5