Final answer:
The best explanation for the decrease in agricultural biodiversity is the practice of monoculture, where farmers grow only one type of crop to simplify operations, potentially leading to environmental issues.
Step-by-step explanation:
The decrease in biodiversity in the agriculture field is best explained by option B: Farmers can yield better results if there is less diversity in the treatment and care of the crops.
This practice, known as monoculture, involves growing a single type of crop over a large area, which simplifies farming operations and can increase efficiency and yields in the short term. However, monoculture farming reduces biodiversity and can lead to a number of environmental issues, such as soil degradation, increased vulnerability to pests, and a loss of genetic diversity among crop species.