一句英语句子求助,这句话应该怎么写?

there are 1000 students in this grade, among which 400 of them are boys 的意思：有1000名学生参与本年级的,其中400是男孩.
there are 1000 students in this grade, among whom 400 of them are boys 的意思：有1000名学生参与本年级的,其中400是男孩.
there are 1000 students in this grade, among who 400 of them are boys 的意思：有1000名学生在这种等级中,他们都是男孩.400.

从这几个句子的意思中,首先排除最后一个,因为“他们都是男孩”表明这1000人都是男孩,而题目说的是其中的400人,那么显然,最后一句不是很正确；那么看第一句和第二句,这两句的关键就在于“among which ”和“among whom ”,"which"是介词加物,就是后面跟的是物体,而“whom”后面指人,后面跟着的单词也应该是人.而题目说是是一个人的整体,大致上来说都是写人,所以,选择第二个句子：there are 1000 students in this grade, among whom 400 of them are boys.
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