问题补充：
it is the first time i have ever been on a stage这个玩意到底是什么时态的?费解死我了,还有就是这个i knew immediately thered been a mistake 这个里面的thered展开是什么玩意?
答案：
主句 It is the first time是一般现在时
从句 I have ever been on a stage是现在完成时
第二句thered展开是there had,这从其后的been就可以判断出来了.
======以下答案可供参考======
供参考答案1:
have done结构是现在完成时时态。后面的句子展开应该是I knew immediately there had been a mistake. had done是过去完成时噢
供参考答案2:
这是我第一次上舞台。
我立刻知道出了一个错误。
供参考答案3:
现在完成时态。
had been a mistake
