there are two things __he was not sure定语从句

there are two things __he was not sure定语从句

此空应该填that,因为先行词things的前面有数词two修饰（请看关于that第（5）个说明）,参考资料如下：
定语从句:在复合句中修饰名词或代词的句子在复合句中充当定语,所以叫作定语从句.
先行词：定语从句所修饰的名词或代词.
关系词：引导定语从句的词,分为关系代词（who,whom,that,which,whose）和关系副词(where,when,why,).
复合句 ：The man who (that) came is Mike.
先行词 关系代词
Li Ming is the one that got full marks in our class.
先行词 关系代词
上句的黑体字为复合句中的主句,蓝体字为定语从句.
一 定语从句的关系代词 Which的用法:若先行词指物则代替先行词在定语从句中充当主语或宾语.
This is the pen which was given by my friend.
先行词 指物代替先行词在定语从句中充当主语
This is the pen which my friend gave to me.
先行词 指物代替先行词在定语从句中充当宾语
二 定语从句的关系代词 Who的用法:若先行词指人则代替先行词在定语从句中充当主语或宾语(如果前面带介词则必须用whom)
The man who is wearing a white suit is my brother.
先行词 指人代替先行词在定语从句中充当主语
The man who\whom he wanted to see last week is in Shanghai.
先行词 指人代替先行词在定语从句中充当宾语
She is the girl with whom I went there.
先行词 指人代替先行词在定语从句中充当介宾且介词于前.
三 定语从句的关系代词 Whom的用法:若先行词指人则代替先行词在定语从句中充当宾语(包括介词的宾语) ,与who的区别是如果前面带介词则必须用whom
This is the teacher whom\who we like best.
先行词 指人代替先行词在定语从句中充当宾语
She is the girl whom\ who I went with there.
先行词 指人代替先行词在定语从句中充当介宾.
I don’t like the boy to whom you are talking.
先行词 指人代替先行词在定语从句中充当介宾且介词于前.
四 定语从句的关系代词 that的用法:若先行词指人或物则代替先行词在定语从句中充当主语或宾语
The animal that \which is lost is a panda.
先行词 指物代替先行词在定语从句中充当主语
She is the person that \who we are worried about.
先行词 指人代替先行词在定语从句中充当宾语
注意1 that \which在代物时常常可以通用,但有时只宜于用which ,不用that
(1) 关系代词前有介词时.
This is the hotel in which you will stay.
(2) 如有两个定语从句,其中一句的关系代词是that,另一句宜于用which.
Let me show you the novel that I borrowed from the liberary which was newly open (新开放) to us.
注意2that \which在代物时常常可以通用,但有时只宜于用that ,不用which.
(1) 先行词是形容词最高级或者它的前面有形容词最高级时
This is the best that has been used against air pollution(反对空气污染) in cities.
English is the most difficult subject that you will learn during these years.
(2) 先行词是序数词,或它的前面有一个序数词基数词修饰时
He is the last person that I want to see.
(3) 主句中已有疑问词时
Which is the bike that you lost?
(4) 先行词既有人又有物时
The bike and its rider that had run over (撞倒了)an old man were taken to the police station.
(5) 先行词是all,much,little,something,everything,anything,nothing,none,the one等代词时
You should hand in all that you have.
We haven’t got much that we can offer you.
I mean the one that you talked about just now.
(6) 先行词前面有only,any,few,little,no,all,one of,the same,the very等词修饰时
The only thing that we can do is to give you some money.
Li Ming is the only one that got full marks (满分)in our class.
Li Ming is one of the students that want to be teachers in our class.
(7) 有两个定语从句,其中一个关系代词已用which,另外一个宜用that
Edison built up a factory(办了一个工厂) which produced things that had never been seen before.
定语从句的关系副词 Where的用法:若先行词指地点且其在定语从句中充当地点状语.
This is the house+I was born in the house.(=I was born there)
介词短语 副词
=This is the house where I was born.这就是我在那儿出生的房子.
先行词 关系副词
in which I was born.
介词+关系代词
which I was born in.
关系代词
这里作介宾的which和that可以省略
that I was born in
关系代词.