题目选项分析

Methane, which has long been counted among the greenhouse gases that are implicated in global warming, comes both from natural sources such as bogs and from a host of human sources, including coal mines, leaking pipelines, landfills, and rice paddies.

Methane, which has long been counted among the greenhouse gases being implicated in global warming, comes from both natural sources such as bogs and from a host of human sources, including coal mines, leaking pipelines, landfills, and rice paddies.