Question

英语选择（定语从句）急急急

He is one of the best swimmers who ( )good at swimming.
A is B are

Answer 1

如果是考试题的话你就只能选B！！

其实实际使用中两者都可使用，但强调的意思不一样！
请看下面的分析：

该句是： “one of+复数名词+关系分句”结构

在“one of+复数名词+关系分句”结构中，关系分句动词通常依照语法一致原则用复数形式。例如：
Joan is one of those people who go out of thier way to be helpful.
I am one of those people who by the general opinion of the world are counted both infamous and unhappy.

但有时为了强调one,这类结构中关系分句动词也可采用单数形式，这种情况在英国英语中比较常见。例如：

Jasper White is one of those rare people who believes in ancient myths.（如题）
My worthy Friend Sir Roger is one of those who is no only ar peace within himself,but beloved and esteemed by all about him.

如果在这类结构之前有定冠词the或者有the only 等限定词和强调词时，关系分句动词形式依one而定，用单数。例如：
Selfishness is the one of her many faults which defears itself.
Keves is the only one of the players who has learned all the players.
He is the only one of those boys who is willing to take on another assignment.

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Answer 2

B

Answer 3

B are
如果是 He is only one of the best swimmers who ( )good at swimming.
这个就选is 这个主语是he

而你的问题主语是后面的那个 the best swimmers.