Question

mittens help keep your hands warm in winter because:
they are conductors of electrical energy.
they are conductors of heat.
they are insulators.
they are fuzzy.

Explanation:

Mittens are made of materials that trap air. Air is a poor conductor of heat (an insulator). This helps to prevent the heat from the hands from escaping into the cold environment outside, thus keeping the hands warm. Electrical conductivity is not relevant to keeping hands warm. If mittens were conductors of heat, they would allow heat to escape, which is the opposite of what is needed. Just being fuzzy does not explain the heat - retaining property; it is the insulating property (related to the material's ability to trap air) that is key.

Answer:

They are insulators.