To solve this question, the user needs to have a basic understanding of computer networking and the functions of different networking devices.

Now, let's go through each option and explain why it is right or wrong:

A. Router: This option is correct. A router acts as a traffic cop in a network. It receives data packets from different devices and determines the best path for each packet to reach its destination. It makes decisions based on network protocols and routing tables.

B. Hub: This option is incorrect. A hub is a basic networking device that simply broadcasts incoming data packets to all connected devices. It does not make any intelligent decisions or act as a traffic cop.

C. Switch: This option is incorrect. A switch is a networking device that connects multiple devices within a local area network (LAN). It forwards data packets to the intended recipient based on the MAC address. While a switch can handle and manage network traffic, it does not perform the same level of intelligent routing as a router.

D. Modem: This option is incorrect. A modem is a device that connects a computer or network to the internet through a telecommunications line. It does not act as a traffic cop within a network.

Therefore, the correct answer is:

The Answer is: A. Router