Concept: The short run is a production period where at least one input cannot be changed.
Explanation: In the short run, not all factors of production can be varied.
At least one factor, such as capital or land, remains fixed.
Other factors, like labour and raw materials, can be adjusted.
This makes option C the correct description.
Options A, B, and D describe either the long run or incorrect changeability conditions.
Answer: C. at least a factor is fixed while others are variable