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What was causing the change in the color of the moths?

the light-colored form of the peppered moth has different genes from the dark form. The black color of the dark form was due to a mutation in the DNA of the light-colored form

50% lit on the left side

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.