--- Do you have any problems _______ your maths?

--- No, I don’t. But I need some help _____ my English.

A．on, on

B．with, with

C．on, with

D．with, on

某二叉树的前序遍历结点访问顺序是abdgcefh，中序遍历的结点访问顺序是dgbaechf，则其后序遍历的结点访问顺序是（）。