Exercício: TOEFL Exam - Gramática

Hi everyone, I am preparing myself to take the TOEFL exam and for this reason I am doing some tests to get more practice.

During my studies, I found a curious question and I would like someone explain to me grammatically the reasons of the answer struct. Follow the question:

xx. which one of the options complete correctly the sentence below?

_________ desert animals are, the more light they reflect

(A) The paler
(B) As pale as
(C) Paler than
(D) Paler as

According to the test answers, the correct option is the letter A. The problem is, it does not make sense to me, because when we use "comparative words", usually is required using the word "than". If in this sentence we use "the superlative words" instead "comparative", it makes sense to me.

Summarizing I am totally confusing about this question and answer, I cannot even elaborate well what my doubt is. I just can not understand the struct of sentence.

Thank you everyone and I already appreciate your attention.