The theory about alien thickness wherein it says that “Alien thickness is mainly affected by temperature. The greater thickness at lower temperatures may be used as a way to stay warmer in colder weather” seems most valid or most accurate.
The correct answer between all the choices given is the third choice or letter C. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.