Carbon dioxide is the primary greenhouse gas emitted by human activities,especially from burning fossil fuels for electricity,transport and industry. Its long atmospheric lifetime and high volume make it the dominant driver of anthropogenic climate change. The stem explicitly links the gas to combustion of coal,oil and natural gas,which clearly points to carbon dioxide. Hence Option A is correct.
Option A:
Carbon dioxide concentrations have been rising steadily since the industrial revolution,enhancing the greenhouse effect. Because of this central role,international climate agreements focus heavily on reducing CO₂ emissions. This explanation fits the description in the question.
Option B:
Methane is also a potent greenhouse gas and arises from agriculture,fossil fuel extraction and waste,but its global emissions from burning fossil fuels are smaller in volume than CO₂. It is therefore not the most significant gas in the specific context described.
Option C:
Ozone acts as a greenhouse gas in the troposphere but is not emitted directly in large amounts from fossil fuel combustion. It is mainly formed as a secondary pollutant,so it does not match the stem as closely as carbon dioxide.
Option D:
Carbon monoxide is a toxic gas produced by incomplete combustion and has health impacts,but its direct greenhouse effect is relatively weak compared to CO₂. Thus it is not the best answer here.
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