This is ______I wanted. A the one what B which C one which D the one

1. D the one

完整的是 This is the one that I wanted

先行词是the one 后面是由that 引导的定语从句，修饰the one

而that在定语从句中，是充当want的宾语，是宾语成分，可以省略掉，所以就变成 this is the one I wanted

如果用A,应该是 This is what I wanted. what引导的一个表语从句

5. B /

as we know, I think, to be honest 等很多词组都是插入语，它们对原来的句子没有影响

这里as we know是插入语，可以把它忽略掉，那剩下的就是 Oxford is one of the best...... 这是一个完整句子了。