Choices A, C, D, and E are all incorrect. These activities affect the organisms and alter the environmental systems.

Choice B is correct. A national park is an area that is built for the purpose of preserving wildlife. It is usually protected by the government. Therefore, it has the smallest impact on the environment.

B. using land to create a national park

Choices A, B, D, and E are all incorrect.
According to the graph, the concentration of ozone-destroying halogens has significantly decreased from 1992 to 2008. This indicates that banning the use of certain chemicals in 1897 has successfully reduced the pollutants in the ozone layer. Therefore, the correct answer is C.

C. The concentration of halogens in the atmosphere decreased during this time period.

Choices A, B, C, and E are incorrect. These activities are contributing to the loss of biodiversity.

Choice D is correct. The process of reforestation involves the replanting of trees in an area that has suffered deforestation. This event can help reverse the ecosystem effects of biodiversity loss.

D. reforestation

Choices A, B, and D are all incorrect. These events do not directly reflect the effect of burning fossil fuels.

Choice C is correct. The ocean becomes more acidic if there is too much carbon dioxide in the atmosphere. As the ocean absorbs carbon dioxide, which is a greenhouse gas, it becomes carbonic acid when it reacts with the saltwater. This results in the rise of acidity in seawater, which weakens the corals and other aquatic species.

C. Increased levels of carbon dioxide in seawater would cause ocean acidification and weaken corals.