Final answer:
As the human population continues to increase, plant and animal diversity is expected to reduce due to habitat loss, increased pollution, and climate change, all of which are intensified by greater numbers of people and their activities.
Step-by-step explanation:
The question posed is related to the consequences of human population increase on the environment. Specifically, the answer to the question is 'd. reduction in plant and animal diversity.' This choice corresponds with the evidence that biodiversity is likely to decline as the human population increases due to factors such as habitat loss, increased pollution, and climate change. Enlarged human populations lead to more land being converted for housing, farming, and industry, which destroys natural habitats. Pollution from various human activities also plays a major role in endangering species. Furthermore, the changes in climate resulting from human activities, such as burning fossil fuels, exacerbate the challenges faced by wildlife and plants, contributing to a further decline in biodiversity.