Final answer:
In the Immediate Short Run, the price level is fixed and represented by a horizontal supply curve. Input prices are fixed while output prices may be flexible.
Step-by-step explanation:
The term Immediate Short Run typically refers to an economic context where certain variables are fixed while others may change. In this case, it appears to assess the nature of economic supply curves. In the immediate short run, typically, the price level is fixed, meaning there is no change in prices in response to changes in demand, which is represented graphically by a horizontal supply curve. Output prices may be flexible to an extent, but input prices are frequently fixed because input costs cannot change quickly (such as contracts for wages). The immediate short run does not feature an upsloping curve, as this would imply rising prices with increased output. A vertical line represents a situation where the output is fixed and cannot be changed no matter the price level, which is not typical for the immediate short run but rather for the long run, as seen in the long-run aggregate supply (LRAS) curve.