第一句：I wouldn't have been punished to sing .（對(duì)過去的事情虛擬語氣要用完成時(shí)呀!wouldn't 用在對(duì)現(xiàn)在時(shí)的虛擬上面哦）
第二句我不太懂你想表達(dá)什么,你是想說我除了唱歌什么也做不了么?如果是的話最好用I couldn't do any ting except singing in class.（這句話是說一個(gè)實(shí)事,為什么你要用虛擬語氣呢?）
第三句：If I had known that I had to sing in class,I would have pretended to be ill at home.（括號(hào)里面這個(gè)一般沒有這么說的,挺奇怪的,感覺意思變成了：我會(huì)一直假裝生病,但是你開始應(yīng)該是沒有跟老師說你病了的吧~所以從何而來你一直假裝自己病了呢,是吧?）但是第一句那個(gè)我想用的是錯(cuò)綜的啊，就是想要主句表達(dá)現(xiàn)在，從句表過去