Which of the following is true for a mean and center line of profile?

• A. When the waveform is repetitive then there is some difference between mean and centre line
• B. Mean line of profile is the mean distance between more prominent irregularities
• C. Mean line profile is the average value of ordinates from mean line
• D. Centre line of profile is the line which is parallel to the direction of profile and area embraced above and below the line is equal