Does the marginal product of labor measure how output changes as wage rate changes, or is it the average product of labor divided through the quantity of capital stock and can it be negative or is it any two of the above? If so which ones? If a company is using a single variable input (labor) and a given amount of a single fixed input (capital) and the level of capital decreases will the total product curve of labor, Average product of labor, or marginal product of labor shift downward or all of the above or none of the above? Also, if a company increases its usage of all inputs by 100% and output increases by less than 100%, is the company's production function exhibiting a decreasing returns to scale, diminishing marginal returns, decreasing marginal rate of technical substitution or any two of the mentioned? If so, which ones?