I need help understanding these concepts

Within the relevant range

A. variable cost per unit decreases as the volume of sales decreases.

B. fixed cost per unit increases as the volume of sales decreases.

C.fixed costs per unit decreases as the volume of sales decreases.

D.variable cost per unit increases as the volume of sales decreases.

Within the relevant range, as the number of units sold increases, variable costs per unit sold are assumed to

A.increase.

B.decrease.

C.remain the same.

When using the scattergraph method to analyze mixed costs, the slope of the resulting line represents the

A.variable cost per unit.

B.fixed cost.

C.opportunity cost per unit.

D.total variable cost.

E.none of these.