The correct answer is C. artificial variable.
An artificial variable is a variable that is added to a linear programming problem to obtain an initial basic feasible solution. It has no physical meaning and is always set to zero in the optimal solution.
A basis is a set of variables that are used to represent the solution to a linear programming problem. A basic feasible solution is a solution to a linear programming problem in which all the variables are non-negative.
An algorithm is a set of instructions that are used to solve a problem.
A basic variable is a variable that is in the basis.
None of the above is not the correct answer because it does not describe an artificial variable.