3My cousin read a history book.__________.A.So John does B.So did John C.So does John D.So J

So did John 和 So John did 的区别在于：前者是 so + 助动词+ 主语表示“也”用于肯定句中,如果是否定句就要用“Neither did John”
后者So John did是so+主语+助动词表示“确实是”重复和肯定的意思.
列句：so+助动词+主语,如
1、He goes to school every day.So do I.他每天上学,我也如此.
2、He is fourteen.So am I.他十四岁,我也十四.
3、He can speak English.So can I.我也会.
对别人情况加以肯定时常用so+主语+助动词
如：1、The students work hard.So they do.同学们学习努力,他们确实努力.
2、He is good at maths.So he is.他善长数学,他确实善长数学.
掌握了他们的用法区别,区分so he does和so does he 也是很容易的事情了.