The moth populations went extinct. The moth populations migrated south. The percentage of light-colored moths in the populations decreased. The percentage of dark-colored moths in the populations decreased.
I gave my students this multiple choice question: A species of moth in England has both a light-colored form and a dark-colored form. In the mid-1800s, the percentage of dark-colored moths increased in areas where black soot from factories covered the trees. The soot in these areas has decreased in more recent times as a result of pollution laws. Which of the following statements describes what has most likely happened to the moth populations in these areas?

Only one answer is correct among these 4 choices:
- The moth populations went extinct.
- The moth populations migrated south.
- The percentage of light-colored moths in the populations decreased.
- The percentage of dark-colored moths in the populations decreased.

Could you tell me which one is correct?

The percentage of dark-colored moths in the populations decreased.