这句It is a secret that I can't tell you.语法正确吗?从语法角度来说,这句It is a secret that I can't tell you.的语法正确吗?如果不正确应该如何修改?（可以的话讲一下that的用法）

这句It is a secret that I can't tell you.语法正确吗?从语法角度来说,这句It is a secret that I can't tell you.的语法正确吗?如果不正确应该如何修改?（可以的话讲一下that的用法）
这句It is a secret that I can't tell you.语法正确吗?
从语法角度来说,这句It is a secret that I can't tell you.的语法正确吗?如果不正确应该如何修改?（可以的话讲一下that的用法）

这句It is a secret that I can't tell you.语法正确吗?从语法角度来说,这句It is a secret that I can't tell you.的语法正确吗?如果不正确应该如何修改?（可以的话讲一下that的用法）
语法没错,但逻辑上句子有问题,
仅仅说 It's a secret 就够了,
因为 secret 已经有 I can't tell you 的含义.
如果你分为两句：
I can't tell you.It's a secret.
那就没问题了.

正确
此处i can't tell you是个定于从句，that可以省略

正确的
it is a secret 是主句
that 后面引导的是定语从句

正确，定语从句 that后面的句子做定语，修饰secret。