What layer sorts out which client and server programs are supposed to get the data?

The transport layer is responsible for determining which client and server programs receive the data. This layer manages end-to-end communication, ensuring that data is delivered to the correct application processes on both the client and server sides. It achieves this through the use of port numbers, which function as unique identifiers for various applications running on a host. For example, while multiple applications might be transmitting data over the same network connection, the transport layer specifies which specific application session the data is intended for by including the appropriate port number in the transport header.

This functionality is critical for applications like web browsers and email clients, which often need to communicate simultaneously over the same network. By managing connections and ensuring that data packets reach the right destination application, the transport layer supports reliable and efficient data transfer.

The other layers mentioned have different roles: the network layer focuses on data packet routing between devices, the application layer encompasses the interface for user applications, and the data link layer concerns itself with physical addressing and framing of data for transmission over a particular medium. Therefore, the transport layer's unique function in directing traffic to the correct applications makes it the accurate choice for this question.