I. 1. We are learning English.
English is being learnt/learned (by us).
2. They grow tea trees well in this soil.
Tea trees are grown well in this soil.
3. I haven't done this exercise.
This exercise hasn't been done (by me).
II. 1. If my grandfather were still alive, he would be hundred today.
2. I ..would have offered to give you a lift if I had had my car yesterday.
3. We wouldn't have any money if we didn't work