According to the law of diminishing marginal returns, we can know that under the condition that other inputs are constant, as the amount of an input increases, the increase in output we get is getting smaller and smaller, but before the marginal cost equals Profitable. As a manufacturer we should:. ['Minimize inputs as much as possible to ensure maximum marginal benefits.', 'Increase inputs until marginal cost equals marginal benefit.', 'Increase investment as much as possible for maximum profit.', 'Maintain a fixed investment.']