单项选择题

Questions 11 to 13 are based on the following talk on greenhouse gas. You now have 15 seconds to read Questions 11 to 13.
Which is the most important greenhouse gas

A．Methane.
B．Carbon dioxide.
C．Oxygen.
D．Helium.

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单项选择题

单项选择题

判断题

Questions 11 to 13 are based on the following talk on greenhouse gas. You now have 15 seconds to read Questions 11 to 13.Which is the most important greenhouse gas