I understand that we can omit words till it becomes ambiguous, but can you give me the proper explanation for not omitting words even when it's not ambiguous?
Eg:
ST1: The practice took in 500$ more in revenue than it did last year. (EMPOWER GMAT)
Why is the above sentence wrong when the [it did] does not exist? (
ST2: The practice took in 500$ more in revenue than last year).
I can feel that it's wrong, but I need a proper methodical approach to tackle the ellipses.
Also this,
ST3: With winter coming, I will have higher bills than last year. (Manhattan SC Guide). How is this correct?
Are all ST1, ST2 and ST3 correct?
I hope you can see my confusion.
Thank you.