None of vs. all of

[English Learner]

ESL/EFL Test "Elementary Grammar Questions", question 6

......... 4 of my grandparents are still alive.

(a) Both
(b) None
(c) All
(d) Many

ESL/EFL Test "Elementary Grammar Questions", answer 6

All 4 of my grandparents are still alive.

Correct answer: (c) All

Your answer was: incorrect
None 4 of my grandparents are still alive.
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Why couldn't I use none? Please explain me!

[Alan]

Hi English Learner,

None 4 of my grandparents doesn't make sense. You would have to say: None of my 4 grandparents ...

Alan
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English as a Second Language
You can read my ESL story Present Simple