Packet-switched networks support pipelining effect.

Pipelining is a technique used in computer science and telecommunications to improve the efficiency of data transmission. It allows multiple data packets to be transmitted simultaneously, overlapping the processing and transmission of data. This helps to reduce the overall latency and increase the throughput of the network.

Packet-switched networks are designed to break data into small packets and transmit them independently over the network. These packets are then reassembled at the destination. This approach allows for efficient utilization of network resources and enables the pipelining effect.

Here's why packet-switched networks support pipelining effect:

1. Packetization: In packet-switched networks, data is divided into small packets before transmission. This packetization process enables the transmission of multiple packets simultaneously. As a result, the pipelining effect can be achieved by overlapping the transmission of different packets.

2. Parallel Processing: Packet-switched networks use parallel processing techniques to handle multiple packets simultaneously. Each packet can be processed independently, allowing for overlapping of data transmission and processing. This parallel processing capability enables the pipelining effect and improves the overall network performance.

3. Store-and-Forward Mechanism: Packet-switched networks employ a store-and-forward mechanism, where each packet is stored temporarily at intermediate nodes before being forwarded to the next hop. This mechanism allows for pipelining by allowing the transmission of subsequent packets while the previous packets are being processed or forwarded.

4. Statistical Multiplexing: Packet-switched networks use statistical multiplexing to share network resources among multiple users. This technique allows for the dynamic allocation of bandwidth based on the traffic demand. By utilizing statistical multiplexing, the network can effectively manage multiple data flows and achieve the pipelining effect.

In contrast, circuit-switched networks establish a dedicated connection between the source and destination before transmitting data. This approach does not support the pipelining effect as the entire connection is reserved for a single transmission at a time.

Similarly, message-switched networks transmit data in the form of complete messages. This approach does not break data into smaller packets and, therefore, does not support the pipelining effect.

Hence, the correct answer is option 'C' - Packet-switched networks.