Frisco Corporation is analyzing its fixed and variable costs within its current relevant range. As its cost driver activity changes within the relevant range, which of the following statements is/are correct?

I. As the cost driver level increases, total fixed cost remains unchanged.

II. As the cost driver level increases, unit fixed cost increases.

III. As the cost driver level decreases, unit variable cost decreases.

1. I, II, and III are correct.

2. I and II only are correct.

3. I only is correct.

4. II and III only are correct.