---Look at that lady on the stage. She is already fifty.
---You are joking. She doesn't look ________
A,so B,it,C that, D the one
答案B，it指代fifty,没问题。
问题是：so，that为什么不可以？
I don't think so.中，so可以作名词，为什么这里就不可以？
that也可以指代年龄啊

答案是 it. 我特地问了我这位美国高级工程设计师先生，他明确了这个说法也没错，it指代fifty，因为我也跟他说我觉得我们通常说she doesn't look like that 或 she doesn't look like it，说 she doesn't look it 真“蹩口”。

至于so, 和 that 的问题，要明确它们在这是作副词功用，后要接形容词才成立。如： she doesn't look so young.
she doesn't look that old.