正确的句子为:Most tree frogs change colors from time to time to fit in with THEIR environment. 将 its 改成 their,因为 这里的主语 frogs 是复数,所以物主代词也得是复数:their (它们的),而 its 的 意思是:它的,与 frogs 不一致.
its environment。改成 their environment 或者 the environment: (Most) tree frogs (change) colors(from time to time)to fit in with (its environment.) 因为句子主语是复数(tree frogs),后面的代词所有格也应该用复数,或者限定性冠词。