i am sorry. i didn't finish my homework (because)

the water is cold. the children can't swim (that)

i can meet you. you arrive before 7p.m (if)

i wrote a letter to my aunt. she lives in Italy (who)

i regret now. i didn't go on a picnic with friends last week (wish)

1. I am sorry because I didn't finish my homework.
-> Clause + because + clause: Quan hệ nhân quả
2. The water is cold that the children can't swim.
-> Cấu trúc "(so)...that....": (quá)...đến nỗi
3. I can meet you if you arrive before 7p.m
-> Clause + if + clause: Quan hệ giả thiết-kết quả
4. I wrote a letter to my aunt who lives in Italy.
-> Đại từ who:
+ Làm chủ từ trong mệnh đề quan hệ
+ Thay thế danh từ chỉ người
+ Công thức: ...N (person) + who + V + O....
5.  I wish I didn't go on a picnic with friends last week. 
-> Công thức: S + wish(es) + V(QKĐ)