ta có cấu trúc since ; for
-> since + 1 mốc thời gian trong quá khứ
-> lưu ý : sau since + thì QKĐ , trước since + thì HTHT
-> for = 1 khoảng thời gian
1 for
2 since
3 for
4 since
5 for
6 since
7 for
8 for
9 since
10 since
11 for
12 since
13 for
14 for
15 since
16 for
17 since
18 for