Stepped fixed costs stay constant within output ranges but increase at key thresholds.

Steps:

• Define fixed costs as unchanging with output volume.
• Recognize stepped fixed costs as fixed but rising in discrete jumps when output hits capacity limits, like adding staff.
• Compare choices: A and B describe variable costs; C matches the "step" behavior; D fits basic fixed costs without steps.
• Confirm C as the precise description.

Why C is correct:

• Stepped fixed costs remain constant until output exceeds a threshold, then jump to a higher fixed level, per cost accounting definitions.

Why the others are wrong:

• A describes variable costs, which vary proportionally with output.
• B repeats variable cost traits, ignoring fixed nature.
• D applies to standard fixed costs, omitting the stepwise increases.

Final answer: C