A medical facility does MRI for sports injuries. Occasionally a test yields inconclusive results and must be repeated. The table below shows the number of retests in eight samples and each sample contains 150 MRI results. The manager needs to select a proper control chart to see if the process is within three-sigma limits. Which of the following statements is correct? Number of retests in each sample are 1, 2, 4, 2, 3, 3, 2, and 1.