倒裝句助動詞had和did的區別

Not until yesterdayhad he changed his mind.

This development，coming as it did when the bottom had fallen

該句型的基本用法為：主語+had hardly done...

when+主語+did...。主句用過去完成時，從句用一般過去時第一句是昨天為止，而不是過去的某個點，是昨天之前的時間段，他從來不知道他這麼能説，所以用過去完成時

這是倒裝句，強調yesterdan，倒回去是He had not changed change his mind until yesterday.這個句子時態要用過去完成時，所以用had.如果你要區分did和had在這類題型中的不同，建議你把2種時態的運用和表達弄清楚.