A a lot about the dangers of extracting natural gas from the earth is known.
B a new research has proved that gas extraction is completely harmless to the environment.
C EPA did not consider the process of natural gas extraction safe.
D the ignorance about the substances that companies use in the process of gas extraction is a complex matter.
E companies do not reveal the chemical mixture they use in the extraction of natural gas, because the American government does not allow them to do so.