In an online billing system, Salesorder Item must have a cost data member that cannot be less than zero. How can you ensure that this condition will be maintained?Define a global variable to store the cost data and a function that checks that the cost is never less than zero. Define a SalesOrder Item class with a public cost data member and add a comment advising programmers that the cost cannot be less than zero. Define a SalesOrder Item class with a private cost data member and define public mutator functions that never let the cost value to be less than zero. All of these options can be used to ensure that the cost is less than zero.