The underwear in the image keeps you warm on cold nights because it a) keeps cold air out. b) is a poor insulator. c) is a good insulator. d) is a good conductor.

Option C,  is a good insulator

Explanation:

See the attached image of the  underwear

Solution

As it is clear in the image, the fabric of the underwear is poly fabric which acts as a good insulator.  

Being an insulator, it can easily trap the heat of the body during winters and does not allow this heat to escape due to which it is successful in keeping a person warm during the winters.  

If the material of the underwear would have been a conductor, it would have allowed heat of the body to escape.

Hence, option C is correct

d

explanation:

the higher the instrument the better