Viết lại câu mà vẫn giữ nguyên nghĩa: The last time we saw her was on Christmas Day

Viết lại câu mà vẫn giữ nguyên nghĩa:
1, The last time we saw her was on Christmas Day.
-> We haven't .........................................................
2, I haven't eaten this kind of food before.
-> This is................................................
3, It started raining an hour ago.
-> It has.......................................
4, When did you start learning English.
-> How long...................................