The correct answer is: B. relevant range
The relevant range is the range of activity within which assumptions about cost behavior are valid. It is the range of activity over which the cost relationship is expected to hold true.
The functional range is the range of activity over which a cost is constant.
The unit range is the range of activity over which a cost is constant per unit of output.
The related range is the range of activity over which two or more costs are related.
Here is a table that summarizes the different ranges:
| Range | Definition |
|—|—|
| Functional range | The range of activity over which a cost is constant. |
| Unit range | The range of activity over which a cost is constant per unit of output. |
| Relevant range | The range of activity within which assumptions about cost behavior are valid. |
| Related range | The range of activity over which two or more costs are related. |
I hope this helps! Let me know if you have any other questions.