Answer: D.All of the above.
Methane is a colourless odourless gas that develops abundantly in nature.
A.Breakdown of plant and animal remains in the soil: The plant and animal remains contains large amount of organic matter, which is decomposed by soil bacteria. This process results in formation of methane gas. The process takes place in the absence of oxygen, hence, called as anaerobic decomposition. This gas gets liberated to the external environment.
B. Leakage from natural gas pipelines: The natural gas is obtained as a fossil fuel from deep layers of the earth. This gas is excavated in order to use it as fuel to run vehicles and for cooking food. The gas may liberate to the external environment by leakage.
C. Food digestion by land animals: The land animals such as cow and buffalo discharge dung, which is a rich source of methane. The methane gets liberated from the cow dung to the external environment.
Therefore, all processes are responsible for liberation of methane to the external environment.
