Hello Xia,
Upon looking at sample 10-4, the displayed poem starts in cell 7 preceded by six blank cells. The reason for this margin is because displayed exercise material starts 2 cells to the right of the previous braille line. In this case, even though there is no braille text on the previous line, if there was the text would begin in cell five.
In the example, the exercise answers start in cell 3 which is the correct format for exercises with subentries.
Thank you
Mike