那句正確?????????????????

正確與否在於個 subject 是 plural (眾數) 或 singular (單數)
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1 They are smart boy.
2 They are smart boys. (CORRECT)
(1)和(2)的 subject也是 plural (they are)
所以 object 也應是 plural = smart boys

3 none of them is a smart boy. (CORRECT)
4 none of them are smart boys. (CORRECT)
5 none of them are smart boy.
Subject 是 "none of them"
"None" 可以是 plural OR singular, 除非句子有其他字指明數子, 否則 plural 或 singular 均可
所以 (3) 和 (4) 正確
(3) 屬 singular 而 (4) 屬 plural
(5) 錯在數量上的予盾 (are 即 plural / boy 則是 singular)
看看解繹
There is one indefinite pronoun, none, that can be either singular or plural;
it often doesn't matter whether you use a singular or a plural verb
unless something else in the sentence determines its number.
Writers generally think of none as meaning not any and will choose a plural verb, as in "None of the engines are working,"
but when something else makes us regard none as meaning not one, we want a singular verb, as in "None of the food is fresh."

None of you claims responsibility for this incident?
None of you claim responsibility for this incident?
None of the students have done their homework. (In this last example, the word their precludes the use of the singular verb.

6 one of them is a smart boy. (CORRECT)
7 one of them are smart boys.
8 one of them are smart boy.
Subject "one of them" 即 "one" 屬 singular
所以 (6) 正確
(7) 錯在 are 和 boys (plural)
(8) 錯在 are (plural)

They are smart boys,
None of them is a smart boy.
One of them is a smart boy.
is correct

那句正確?

2 They are smart boys.(正確)

4 none of them are smart boys.(正確)

7 one of them are smart boys.(正確)

These are correct.

1 They are smart boy. should be HE IS A SMART BOY.

2 They are smart boys.

3 none of them is a smart boy.

4 none of them are smart boys

5 none of them are smart boy. Either 3 or 4.

6 one of them is a smart boy.

7 one of them are smart boys

8 one of them are smart boy. Either 6 or 7.