After all, on the first day of class all you did was talk about...

on the first day of class all you did 是主语，was作谓语
所以。。。

all you did 是个定语从句，在句子里做主语的。 was 是谓语

all you did是主语，was是谓语，但是宾语是talking about，应该是动名词作宾语，我觉得错了

这里的did不能独立的看，all you did（所有你做的事）是整个做主语的，希望可以帮到你哈～要是觉得有用最好加点分哦呵呵，学习顺利哈

all you did 是the first day of class 的定语从句呀，引导词that省略了， on the first day of class all you did 作主语 ，意思是“你们在上课的第一天要做的事是谈论...。”