For more comprehensive worksheets, you can download these common grammar guides: British Council - Substitution and Ellipsis (PDF) Cambridge English - Advanced Grammar Exercises

In a digital age, why focus on PDFs? Because PDFs offer unique affordances for grammar training:

Using auxiliary verbs (do, does, did) for substitution.

When you search for you are looking for a resource that saves time and provides systematic practice.

She could have left earlier, but she didn’t leave earlier. → _________________________________________