Answer: B. Carbon dioxide
Explanation: Global warming arises due to the emission of gases which are accumulated in the atmosphere, that is, the layer of these gases increases in an atmosphere, and prevents the reflected sun rays from the ground to leave the atmosphere. Such a higher amount of sunshine-heat which is higher than necessary, remains in the atmosphere and heats the surface of the earth, which is the effect of the greenhouse. These are gases produced by combustion of fossil fuels, and during this combustion they are emitted into the atmosphere. Gases that cause the greenhouse effect are carbon dioxide, methane and nitrous oxide. The problem is that fossil fuels are used to produce electricity, in agriculture and transport. Global warming has drastically increased over the past decades, and if preventive measures which involving the use of alternative fuels are not undertaken, the catastrophic consequences, which are already visible, will be even greater.