I am trying to figure out when do we need to use an action verb explicitly and when can we omit it using the (ellipsis concept). For Example:
- John is taller than Jim [is] (I understood that here is can be omitted)
- John left earlier than Jim [did] - is it ok to omit the word 'did' - if not, why?
- Maple trees shed their autumn leaves earlier than oak trees - Is this correct?