Understand the concept of a short-run production function: In microeconomics, the short-run is a period during which at least one input in the production process is fixed, while others can be varied.
Identify the fixed and variable inputs: In the short-run, typically capital is considered a fixed input, while labor is a variable input that can be adjusted to change the level of output.
Analyze the given options: The problem provides several statements about the short-run production function. Evaluate each statement based on the definition of the short-run.
Evaluate option (a): 'The level of output is fixed' is incorrect because in the short-run, output can change by varying the variable inputs.
Evaluate option (b): 'The usage of at least one input is fixed' is correct as it aligns with the definition of the short-run where at least one input (e.g., capital) is fixed.