Final answer:
A firm's demand curve for labor shifts due to factors such as changes in the product's price, production process variations, and changes in government policy, not changes in the wage rate which cause movement along the curve.
Step-by-step explanation:
The firm's demand curve for labor will shift due to several factors other than changes in the wage rate. According to economic principles, an increase or decrease in the wage rate causes a movement along the demand curve, not a shift. Factors that may lead to a shift in the labor demand curve include: a change in the product's price, which affects the quantity demanded of the product labor produces; changes in the production process that use different amounts of labor; changes in government policy regarding labor; and variations in other determinants such as technology, workers' education and training, the number of firms in the market, and the price and availability of other inputs.
Choices b, c, and d from the options provided do not lead to a shift in the demand curve for labor. Instead, b could potentially influence the supply of labor, while c and d represent movements along the demand curve rather than shifts.