In a typical network configuration, users and servers require a default gateway to communicate with devices on different networks or subnets. The default gateway is usually the router's interface on the same network, which routes the traffic to other networks. This is essential for the two users to access the remote server if the server is on a different subnet, which is indicated by the different network addresses.

The Routing Engine (RE) in Junos OS has several critical functions, including processing all management traffic (A) and running the Junos operating system (B). The RE handles system management tasks, user interfaces, system services, and routing protocol processes. It does not directly process transit traffic or evaluate firewall filters for transit traffic, as these tasks are handled by the Packet Forwarding Engine (PFE).

To view real-time usage statistics for the busiest interfaces on a device running Junos OS, the correct command is B, "monitor interface traffic." This command provides a dynamic, real-time view of the traffic flowing through the interfaces, allowing administrators to quickly identify and monitor the busiest interfaces on the device.

To convert the decimal number 7 to binary, the correct representation is 00000111 (C). In binary, 7 is represented as 1+2+4 (2^0 + 2^1 + 2^2), which corresponds to the last three digits being 1 in the binary format, with leading zeros added for clarity.

Implementing Class of Service (CoS) in a network provides numerous benefits, particularly in managing traffic based on its importance, source, or type. CoS enables network administrators to manage traffic congestion by applying various queuing techniques and policies to ensure that critical services remain unaffected during high congestion periods. Additionally, CoS allows for the prioritization of latency-sensitive traffic such as voice and video, ensuring that these services maintain quality despite varying network conditions.