According to Rosemary Stewart, involve(s) activities or duties that must be accomplished and standards or levels of minimum performance that must be met.

Demand

Explanation:

 The demand is the term which is used to refers to the quantity of the products that the customers are willing or desire to purchase at the various types of given prices.

The demand curve is explained as the relationship between the demand of the given products in the market and the product price and this curve is also varying based on the factors such as price and demand of the goods and the services.

According to the rosemary Stewart the demand is basically involve the various type of  activities and the duties that helps in accomplished the performance.  

 Therefore, Demand is the correct answer.