A blind man cannot distinguish light _____ darkness.

A. between
B. from
C. with
D. to

In English grammar, prepositions are used to show the relationship between words in a sentence. They often indicate direction, location, time, or other relationships. In the given sentence, the correct preposition to use is “from” as it shows the relationship between “light” and “darkness” in terms of distinguishing one from the other.

Therefore, the correct answer is “from.”