Because the book was wrote in English, so I told him to use the (A1), (A2),(A3) and (B1), (B2), (B3) and (C1),(C2),(C3) etc as the mark of level.

• 因为这本说明书是英文的，所以我教他用（A1）（A2）（A3）和（B1）（B2）（B3）（C1）（C2）（C3）作为各级分段的标记。