The correct answer is D. In all areas of production.
The law of diminishing returns states that in all productive processes, adding more of one factor of production, while holding all others constant, will at some point yield lower incremental per-unit returns.
This law applies to all areas of production, including agriculture, industry, and services. In agriculture, for example, adding more fertilizer to a field will eventually lead to lower yields, as the soil becomes saturated with nutrients. In industry, adding more workers to a production line will eventually lead to lower output per worker, as the workers become more crowded and less efficient. In services, adding more employees to a call center will eventually lead to longer wait times for customers, as the employees become more stressed and less productive.
The law of diminishing returns is a fundamental principle of economics, and it has important implications for how businesses and governments make decisions about production. For example, businesses need to be aware of the law of diminishing returns when they are deciding how much to produce. If they produce too much, they will end up with lower profits. Governments also need to be aware of the law of diminishing returns when they are deciding how much to spend on public goods. If they spend too much, they will end up with lower levels of output.
The law of diminishing returns is a powerful tool for understanding the economics of production. It can help businesses and governments make better decisions about how to allocate their resources.