The most likely statement to explain the change in the proportion of green toads from 20% to 50% over 50 years is:
O The environment changed such that green toads can blend into their surroundings better.
This explanation suggests that the increase in the population of green toads could be due to a change in the environment that favored their camouflage, making them less visible to predators and thus increasing their survival and reproductive success compared to brown toads.