The demand curve for labor would shift leftward as the result of:

A) an increase in the price of the product labor is producing.
B) a decrease in the productivity of labor.
C) an increase in the price of labor.
D) a decrease in the price of capital,provided the output effect exceeds the substitution effect.

A decrease in the productivity of labor would result in a decrease in the demand for labor as firms would require less labor to produce the same amount of output. An increase in the price of the product labor is producing (A) would lead to an increase in demand for labor, as firms would require more labor to produce more output. Increase in the price of labor (C) would lead to a decrease in the quantity of labor demanded, but it would not shift the demand curve leftward. Similarly, a decrease in the price of capital (D) may lead to a decrease in the demand for labor, depending on the relative substitutability of labor and capital, but it would not shift the demand curve leftward.