Hi Happy,
This area is a very contentious one, so it is not surprising that you find different pronouncements within and between grammar books. Here is my opinion on the examples you present:
(1) 'Who did it ?' Not I.'
The pronoun stands in parallel to the subject 'who', and is a...
ESL General English Grammar Questions
by
Mister Micawber
4 yr 47 days ago
American English, Grammar, Verbs, Plurals, Prepositions, Clauses, Nouns, Pronouns, Subjunctives, Whom, Nominative, Conditionals, Contractions