Final answer:
The United States is the largest producer of corn globally due to optimal soil and climate conditions, advanced farming techniques and technology, and favorable agricultural policies and subsidies. Therefore, the correct option is d.
Step-by-step explanation:
The United States is the largest producer of corn globally due to a combination of factors. Firstly, the US has optimal soil and climate conditions for corn production, allowing for high yields. Secondly, advanced farming techniques and technology, such as mechanization and irrigation, have greatly improved efficiency and productivity in corn farming. Lastly, the US government provides favorable agricultural policies and subsidies for corn production, which further support the industry.