指人可用that who, 以下情况多用who;

Those people做先行，There be的结构中;

例句：

1) Those who are for the plan, please raise your hands.

赞成计划的人请举手。

2) People who create computer viruses are called hackers.

制造电脑病毒的人被称为黑客。

3) There was once a little boy who came to the net bar to play games every night.

曾经有一个小男孩每天晚上都来网吧玩游戏。

先行指人不定代，从中做主who要在;

先行词是指人的不定代词，如 one 、someone 、anyone、nobody 等词，或指人的关系代词在定语从句中做主语，要用who, 而不用that。

更多定语从句讲解  ,语法学习 http://www.tingclass.net/show-113-328135-1.html

 

例句：

1)Nobody who knows a little scientific knowledge will believe you.

懂得一点科学知识的人都不会相信你的话。

解析：nobody是指人的不定代词，用who, 不用that。

2)The thief who pretended to be a manager was caught stealing a car.

那个装扮成经理的贼在偷车时被当场抓获。

解析：who指人，在定语从句中做主语。

两个定从一起来，不要重复你有才;

一个先行词有两个定语从句时，关系代词要避免重复使用。

A plant that can cure diseases, which was known by the ancient Chinese , is called Chinese herbal medicine. 一种能够治病的，被古代中国人所熟知的植物，叫做中药。