核心问题
（1）It is I who ____ (am/is) to blame. (2) It is you who ____ (are/is) to blame. 我不知道哪个用法是正确的。
词典解答
正式用法是：It is I who am to blame. It is you who are to blame. 非正式用法是：It is me who/that is to blame. It is you who/that is to blame.
（1）It is I who ____ (am/is) to blame. (2) It is you who ____ (are/is) to blame. 我不知道哪个用法是正确的。
正式用法是：It is I who am to blame. It is you who are to blame. 非正式用法是：It is me who/that is to blame. It is you who/that is to blame.