Which of the following best describes a step variable-cost function? A) A step cost function in which cost remains the same over narrow ranges of the level of activity in each relevant range B) A step cost function in which cost remains the same over narrow ranges of the level of activity outside the relevant range OC) A step cost function where the cost remains the same over wide ranges of the activity in each relevant range D) A step cost function where the cost remains the same over wide ranges of the activity outside the relevant range