What were the theories for why the moths were changing color?

Genetic Changes

Moths passed their color to the next generation. Eggs from light moths developed into light moths and dark moth eggs turned to dark adults. The dark color was caused by a mutation in the DNA of a single moth, and the mutated gene had been passed to all its offspring.

In 1850 There were 23 light moths for each dark one whereas in 1900 the ratio is one light to 23 dark. Thus, if natural selection was responsible for the change in population, according to Darwin's theory, dark moths must have been better adapted to their environment. Gosh humans are destroying the ecosystem.

i am positive it is c. condensing but i may be wrong