it is not_______ i won't do it,_____ i can't do it.
分析一下答案：because,but that.谢谢

个人认为(that,but that) ; (because, but because)或者
(because, but that)均正确。原因如下：

【1】that 本身也可以“引导状语从句, 表示原因或理由”，翻译为因为, 由于。
Not that I'm unwilling to go with you, but that I'm busy now.并不是我不愿意和你去, 而是因为现在我很忙。

【2】because 就更不必说了。
I did it not because I liked it but because I had to do it.我坐这个不是因为我喜欢，而是因为我不得不这么做。
I criticized him, not because I hate him but because I love him.我批评他不是因为我恨他而是因为我爱他。

【3】所以说：
not because....but because...=not that....but that...
不是因为...而是因为...

供参考！