Labour cost is the second element of ________.

The correct answer is A. cost.

Labour cost is the second element of cost, after material cost. It is the cost of the labour used in the production of goods or services. Labour cost includes the wages and salaries paid to employees, as well as the cost of benefits such as health insurance and retirement contributions.

The other options are incorrect. Profit is the difference between revenue and cost. Sales is the revenue generated from the sale of goods or services. Task is a unit of work that is assigned to an employee.