1. The last time we saw her was on Christmas day
⇒ We haven't seen her since Christmas day
2. I haven't eaten this kind of food before
⇒ It is the first time I have ever eaten this kind of food
3. It started raining an hour ago
⇒ It has rained for an hour
4. We haven't visited my grandfather for two months
⇒ The last time we visited my grandparents was two months ago
5. I have studied English for three year
⇒ I started studying English three year ago