she was the one picked the fight.这句话是不是错的？

是不是应该改为she was the one that picked the fight.啊？

因为the one 后只能由that作引导词是吗？而且这里picked the fight少了一个主语是吗？

that作主语时是不能省略的是吗？

你的理解是正确的

用定语从句作后置定语表达如下：

She was the one that/who picked the fight.

用不定式作后置定语表达如下：

She was the one to pick the fight.

pick a/the fight with  寻找…的口实；寻（衅）；找（碴儿）

He picked a fight with a waiter and landed in jail.

他找碴儿跟服务生打了一架，最后进了监狱。

He was clearly in a mood to pick a quarrel with anybody. 

他现在的心情明显是逮谁就想跟谁吵。

the one指人时，作主语后面除了that也可接who作关系词吗？

回答为YES,是的

如果the one指物时，也可以用which和that作关系词是吗？

回答：如果先行词表示人的不定代词，用关系代词that/who都可以;如果指物，只能用关系代词that，不能关系代词which.

为什么我看语法书上说：指人时，当先行词是one,ones,anyone或those时，关系代词用who.

指物时，当先行词为all,much,等不定代词时用that的?

继续回答如下：

当先行词为不定代词one, anyone,表示人的时，首选用who,当然用that也是可以的，但是如果指物，就只能用that不能使用其他关系代词引导定语从句。

以下是我以前解答问题，请查看（也可以点击链接地址直接打开）

http://ask.yygrammar.com/q-21782.html

老师您好！我有两个问题：

He is the only one of the students who have been abroad.

  1.这句话中的have是不是需要改为has?

  2.为什么在上面的定语从句中要用who而不是that？（原因是：英语语法关于定语从句中讲到，先行词被the only修饰的话，只能用that来引导定语从句，而不能用who或其他引导词引导.）

回答如下

(1)是需要改为单数，因为，关系代词who指代先行词为the only one不是the students.

This is the only one of the best novels that has appeared this  year.

(2)如果先行词为the only one，如果指事物用关系代词that 引导定语从句，如果指人，用who 引导定语从句。

He was the only one of the  boys who wasgiven a prize.

(1)the only one of the +名词复数，后面关系引导定语从句谓语用单数。因为定语从句主语为“the only one” 因此谓语用复数.

Mary is the only one of the youngest girls who plays in the band.

玛丽是参加乐队伴奏的最年轻的姑娘。

(2)one of the +名词复数，后面关系引导定语从句谓语用复数,因为定语从句主语为“名词复数” 因此谓语用复数.

This is oneof the rooms that were damaged in the fire.

这就是那次大火烧毁的房间之一。

继续跟踪回答如下：

这位同学看得出来，对知识很具有钻研精神，这点非常好的！关于你的这个问题，可能你的老师没有给你讲清楚，当先行词被the very,the only,the last, 以及序数词，形容词最高级修饰时，要用关系代词that引导定语从句时针对于关系代词which来讲的，不是关系代词who,而且先行词指代代替事物的条件

只能用关系代词that 引导定语从句不能用关系代词which,条件如下

关系代词指代某物事时，只用that不用which的情况

最大条件关系代词所代替的名词只能是表示“事物”的名词 或者“人+事物”的名词；其它条件如下：

(1)当先行词是everything, anything, nothing 。 all, none, few, little, some等不定代词时，或当先行词受every, any, all, some, no, little, few, much等词修饰时。

Is there anything that I can do for you?

Do you have anything that you say to me ?

(2)先行词被序数词或形容词最高级修饰时。

This is the most beautiful place that I have ever visited.

(3)先行词被the very，the only，the right，the first，the last等修饰时

This is the last thing that I want to tell you.

(4)先行词前有the same 修饰时

This is the same pen that I lost last night.

(5)如果表示和先行词是同一物时用the same…that…

This is the same purse that I lost yesterday.

这就是我昨天丢的那个钱夹。

(6)如果表示与先行词同一样的某物

This is the same purse that I lost yesterday.

这个钱夹和我昨天丢的那个一样。

(7)先行词是并列结构，既有人又有物时

He can remember the things and the persons that he met on his trip.

(8)先行词为数词时

Look at the books on the bookshelf. You can see the two that you bought me for my birthday.

(8)避免重复原则，当先行词前面有who, which等疑问代词时

Which is the pen that you need?

(9)关系代词在定语从句中作表语时，而且通常省略

My hometown is no longer the place that it used to be.

如果还有疑问，请继续追问，如果满意，请采纳，谢谢！