题目内容：

四道英语句型转换,
1.What you have done does harm to the environment.
What you have done _____ _____ _____/ _____ _____ _____ the environment.
2.When do you think this custom began to exist?
When do you think this custom _____ _____ _____?
3.I study hard so that I may not fail in the examination.
I study hard _____ _____ _____ _____ / _____ _____ _____ _____ fail in the examination.
4.I don't know it exactly.
I don't know it _____ _____.