TOEFL Reading: ETS-TOEFL阅读机经 - RZY65SF6597667AHL$

According to paragraph 3, why are gas hydrates a possible threat to the global climate? A. If disturbed by offshore drilling, they can destroy limestone deposits. B. They can replace regular ice at certain locations. C. If melted, they may release a lot of carbon dioxide into the atmosphere. D. They contain a lot of methane, which may be released as the ocean warms