whom什么时候用？
each of whom在句中做非限制性定语从句时候用。中文意思是“每个……”例如，运动场上今年高三体育生们正在积极训练考试项目，他们每个人都在为实现大学梦想而拼搏。
On the playground, this year's senior three physical education students are actively training the test items, each of whom is fighting for the realization of their college dreams.
