Công thức : S + had + PT2 + O
Dấu hiệu nhận biết :
-Từ nhận biết: until then, by the time, prior to that time, before, after, for, as soon as, by, ...
-Trong câu thường có các từ: before, after, when by, by the time, by the end of + time in the past …
Eg : - When I got up this morning, my father had already left.
- By the time I met you, I had worked in that company for five years.
#nocopy
