Secondary environmental problems are caused by human activities and are divided into two categories: environmental pollution and ecological damage. Environmental pollution is the direct or indirect discharge of substances or energy beyond the self-purification ability of the human, which deteriorates the quality of the environment and destroys the ecology. System and people's living environment; ecological damage is caused by human activities directly acting on the natural environment. According to the above definitions, Which of the following are environmental pollution:. ['The uneven distribution of water resources in the region has further exacerbated water stress.', 'Soil and water loss caused by vegetation damage, polluted water quality affects the ecological balance.', 'Land desertification caused by large-scale reclamation of grasslands, reducing land area and output.', 'Harmful light blue smoke generated by carbon dioxide emitted from automobiles under the action of ultraviolet rays.']