1What did you buy.这是特殊疑问句,代词What 做主语,这种句式倒装.
2,Speaking 是动名词当主语.谓语是mean,宾语是动名词doing,does not 表否定修饰谓语.
3,the train had left 是真正的主句,
3Bye the time I got to the station可以理解为表时间的状语从句,
I got to the station,可以理解为Bye the time的定语.