In this dialogue:
A: 现在恢复得怎么样了?
B: 没问题了,又可以爬山了。
Why is 又 used there and not 再?
As far as I know (I might be wrong), both 再 and 又 are used for describing recurring actions, but 又 refers to actions that took place in the past and 再 refers to future actions. So in the example, 可以爬山 (I can climb mountains) seems a future event (needs to go to a mountain first).