现有4个文档： 文档1：I know. 文档2：You know. 文档3：I know that you know. 文档4：I know that you know that I know. 试计算，文档3中的that的TF-IDF值
A、0.2ln(3)
B、0.2ln(2)
C、0.3ln(2)
D、0.3ln(3)