The correct answer is C. transport.

The transport layer is responsible for packet sequencing, acknowledgments, and requests for retransmission. It ensures the reliable delivery of data between two hosts and establishes end-to-end connections, if required. The transport layer protocols, such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol), handle these functions.

Now, let's go through the other options and explain why they are not the correct answer:

A. network: The network layer is responsible for routing and forwarding packets across different networks. It does not handle packet sequencing, acknowledgments, or retransmission.

B. session: The session layer is responsible for establishing, maintaining, and terminating sessions or connections between applications. It does not handle packet sequencing, acknowledgments, or retransmission.

D. data link: The data link layer is responsible for the reliable transfer of data frames between adjacent network nodes. It does not handle packet sequencing, acknowledgments, or retransmission at the packet level.

E. presentation: The presentation layer is responsible for data formatting, encryption, and compression. It does not handle packet sequencing, acknowledgments, or retransmission.

Therefore, the correct answer is C. transport.