I have bought such a watch ( ) was advertised on

I have bought such a watch ( ) was advertised
on TV.
A.that B.which C.as D.it
答案是c 为啥 详细点

选C,　属于定语从句,先行词被such修饰时,such 后一般可以接that 或as .
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本题定语从句( ) was advertised in TV中缺少主语.要用用关系代词as引导.
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如果要使用such... that ...时,that后应是一个完整的句子.

c

as 在这儿是关系代词，代替watch 在后面句子中作主语。as到句末是一个定语从句。

句中有such...所以后面的定语从句用as, 句子的意思是：我已经买了电视广告中的手表。 as引导的定语从句可以用在such...as, the same .. as, so..as, as..as的结构中。 如： He is not the same guide as showed the foreigners around our city a few days ago. 他不是前天带领外宾参观我们城市的那个导游。 This is not so easy a problem as everyone can work out. 这题目并不容易， 不是人人都能解出的。