Her health _____ under the pressure of work and she had to stay in hospital for a month. [ ]

A. broke up

B. broke down

C. broke out

D. broke away

下题基于如下所示的二叉树。

如果将该二叉树存储为对称序线索二叉树，则结点C的左线索指向哪一个结点（）。

A．结点A

B．结点B

C．结点E

D．结点G