What does the expression "impossible" imply about a task's completion?

The expression "impossible" indicates that the task cannot realistically be completed within the parameters given, such as time constraints or resource availability. Option C correctly captures this meaning by stating that the task is unrealistic to finish in a set time. When something is labeled as impossible, it suggests that no matter the effort or approach taken, the completion of the task is beyond reach due to its demanding nature or the limitations involved. This interpretation aligns perfectly with the notion of practicality and feasibility, which option C emphasizes.