please explain!

1. Tor F: Within the relevant range, a change in activity results in a change in total variable costs and a change in the fixed cost per unit. 2. Tor F: Mixed costs per unit decrease as volume increases because of the fixed cost component. 3. Tor F: When graphing total mixed costs, the cost line begins at the origin 4. Select the correct answer: A is a fixed cost; B is a variable cost During the current year the level of activity has decreased but is still within the relevant range. We would expect that: a. The cost per unit of A has decreased b. The cost per unit of A has increased c. The cost per unit of B has decreased d. The cost per unit of B has increased