Which of the following is a characteristic of an insulator?

The defining characteristic of an insulator is its ability to restrict the movement of electrons. Insulators are materials that do not allow electric charges to flow freely, which means that they inhibit the transfer of electricity. This property makes them essential for protecting against electrical shocks and ensuring that current flows only through intended pathways, such as wires.

In contrast, good conductors of heat and electricity are typically materials that allow for the easy flow of electrons. These would not exhibit the properties of an insulator. Therefore, the characteristic that accurately describes an insulator is its role in limiting electron movement, making option C the correct choice.