The correct answer is: C. Declining total production.
The law of diminishing returns states that in all productive processes, adding more of one factor of production, while holding all others constant (ceteris paribus), will at some point yield lower incremental per-unit returns. The law of diminishing returns does not imply that adding more of a factor will always decrease the production, just that the marginal (additional) output per unit of the factor will eventually decrease.
Option A, inelastic production, is incorrect because it refers to a situation where the quantity demanded of a good does not change much in response to a change in price.
Option B, negative marginal production, is incorrect because it refers to a situation where the marginal product of a factor is negative. This can happen if the factor is being used in such a way that it is actually causing a decrease in output.
Option D, declining average production, is incorrect because it refers to a situation where the average product of a factor is decreasing. This can happen if the factor is being used in such a way that the marginal product of the factor is decreasing.
In conclusion, the correct answer is: C. Declining total production.