Which two greenhouse gases have human activities notably increased?

The correct choice identifies carbon dioxide and methane as the two greenhouse gases significantly enhanced by human activities.

Human activities, such as the burning of fossil fuels for energy, transportation, and industrial processes, have led to a substantial increase in carbon dioxide levels in the atmosphere. Deforestation and land-use changes also contribute to increased carbon dioxide because trees, which naturally absorb this gas, are removed.

Methane, on the other hand, has seen notable increases primarily due to agricultural practices, such as livestock production and rice cultivation, as well as from landfills and the natural gas industry. Methane is a potent greenhouse gas, with a much greater heat-trapping ability than carbon dioxide over a shorter timeframe.

The other options provided mention gases that either do not have significant human-induced increases or do not primarily result from human activities. For example, ozone is generated naturally and can also be a product of human activity, but it is not emitted directly like carbon dioxide and methane. Sulfur dioxide, though linked with industrial processes, doesn't have the same impact on global warming as greenhouse gases do. Water vapor is a naturally occurring gas and increases in the atmosphere are largely driven by natural processes rather than direct human emission.