Transport Layer
The correct answer is option C, which is the Transport Layer. The division of a message into segments is a function of the Transport Layer in the OSI (Open Systems Interconnection) model.

Role of the Transport Layer
- The Transport Layer is responsible for end-to-end communication and ensuring that data is delivered error-free and in the correct order.
- It breaks down the message received from the upper layers into smaller segments for transmission over the network.
- These segments are then transmitted individually and reassembled at the receiving end to reconstruct the original message.

Segmentation and Reassembly
- Segmentation is the process of dividing the message into smaller segments for efficient transmission over the network.
- Each segment is given a sequence number to ensure that they are delivered in the correct order.
- At the receiving end, the Transport Layer reassembles the segments into the original message based on the sequence numbers.

Benefits of Segmentation
- Segmentation allows for more efficient transmission of data as smaller segments can be transmitted more quickly and reliably.
- It also helps in managing network congestion as smaller segments are easier to handle and route through the network.
In conclusion, the division of a message into segments is a crucial function of the Transport Layer in the OSI model. This process ensures reliable and efficient communication between devices on a network.