核心问题
章振邦教授主编的《新编英语语法》(上册)(上海译文出版社,p.179)强调指出：“在everybody, anybody, everyone, anyone等词后面只能用关系代词 who。”但是我却读到过这样的句子：Everyone that knew him liked him.
词典解答
PEG第三版(1980)对于这个问题曾作过明确的解释：
“在通常情况下,用作主语的 that 远没有 who 那么常用,但是,在形容词最高级之后以及在 all, nobody, no one, somebody, someone, anybody 等词之后,既可以使用 who,也可以使用 that:
He was the best king who/that ever sat on the throne.
All who/that heard him were delighted." (PEG, p. 44)
PEG 第四版(1987)作了更加明确的说明：
“在 all, everyone, everybody, no one, nobody 和 those 之后也可以使用 that 作关系代词……”