At low temperature, a semiconductor virtually behaves like ______.

Correct option is C

 At low temperatures, the thermal energy available to the electrons in a semiconductor is very low.
 This means that very few electrons have enough energy to jump from the valence band to the conduction band, where they can contribute to electrical conduction.
 As a result, the number of free charge carriers (electrons and holes) in the semiconductor is very small, causing it to behave almost like an insulator.