What type of chart displays the upper and lower limits of a variable's statistical significance?

The control chart is the correct choice because it is specifically designed to monitor a process over time and to identify any variations that may indicate a deviation from the expected performance. The chart includes upper and lower control limits, which signify the thresholds of acceptable variation in a given process or variable. By plotting data points over time on this chart, project managers and quality control teams can visually ascertain whether the process is in a state of statistical control or if corrective action may be needed when points fall outside of these limits. This makes it a crucial tool for project management and quality assurance, enabling teams to maintain performance standards and manage risks effectively.

On the other hand, flowcharts serve to visualize the steps in a process, Gantt charts are used for scheduling project tasks over time, and data flow diagrams depict the flow of data within a system. None of these options focus on statistical significance or include control limits, which solidifies the control chart as the only suitable answer.