Stop-and-Wait is a flow control method where the sender transmits a single frame and waits for an acknowledgment before sending the next frame. It is a simple method but not very efficient as it has a high overhead due to frequent acknowledgments.

WAN (Wide Area Network) would be most appropriate for interconnecting offices across continents. WANs cover a vast geographic area, making them suitable for connecting networks in different cities, countries, and even continents. They provide the necessary infrastructure for global connectivity, such as the internet.

ARP poisoning is a concern when an attacker tries to impersonate another device on the network by poisoning the ARP cache of the target device. This can lead to man-in-the-middle attacks, where the attacker intercepts and potentially alters network traffic. Network administrators need to be vigilant in detecting and preventing ARP poisoning attacks.

Mesh topology provides the highest fault tolerance due to its multiple connections. In a mesh network, every device is connected to every other device, ensuring redundancy. If one connection fails, traffic can be rerouted through other paths. This makes mesh topology highly fault-tolerant. However, it can be expensive and complex to set up due to the number of connections required.

The correct option is "Type." In Ethernet frame structure, the "Type" field specifies the type of protocol being used within the frame. This field helps network devices determine how to interpret the data within the frame, whether it's IP, ARP, or another protocol.

Quadrature Amplitude Modulation (QAM) is a modulation technique that combines both amplitude and phase modulation. It uses both amplitude and phase shifts to encode multiple bits per symbol, allowing for higher data rates and more efficient use of the spectrum. This is in contrast to basic amplitude or frequency modulation, which use only one of these characteristics for modulation.

In a MAC (Media Access Control) address, the first three octets are known as the OUI (Organizationally Unique Identifier), and they identify the manufacturer or organization that produced the network card. This allows for unique identification of devices on a network.

The first message sent by the client during the three-way handshake is the SYN (Synchronize) packet. It is used to initiate the connection setup process by indicating the sequence number for data exchange and request a response from the server.

The AS Path attribute in BGP (Border Gateway Protocol) is used to prevent routing loops. It's a list of AS (Autonomous System) numbers that a route has traversed. By checking the AS Path, BGP ensures that routes do not go through the same AS more than once, thus preventing loops.

Modulation is necessary in data transmission to increase the speed at which data can be transmitted over a communication channel. Modulation is the process of encoding digital data onto an analog signal, allowing it to be transmitted over long distances with minimal loss of signal quality.