Explanation:
For packet networks to support multiple and diverse applications, the following requirements are necessary:
1) Transfer arbitrary message size: Packet networks should be capable of handling messages of varying sizes to accommodate different types of applications.
2) Low delay for interactive applications: Packet networks should strive to minimize delay to support interactive applications such as real-time communication and online gaming.
3) Packets have maximum length: Implementing a maximum length for packets ensures efficient use of network resources and prevents the transmission of excessively large packets that could degrade network performance.
Therefore, the correct answer is:
4) All of the above