What does a throughput tester do?

A) Locate faults in a cable
B) Identifies which pair of wires connects back to an end user's location
C) Observes how a network performs under a heavy load
D) Prevents static discharge from damaging other components

C
Explanation: Networks often perform differently when they are under a heavy load, as opposed to little or no load, which might be the case if you are mocking up a design in a testbed environment (which is a test network isolated from any production network). Also, you might simply want to verify a network's maximum throughput. Either scenario could benefit from a throughput tester. A throughput tester is a network appliance, which typically has multiple network interfaces and can generate high volumes of pseudo-random data. You could, for example, connect a throughput tester to a proposed network that has been mocked up in a test bed, to observe how the network performs under a heavy load. Also, you can attach a throughput tester to a production network to determine the actual throughput of that existing network.