谁知道这道英语题?Is this car the one you bought last winter?为啥不用关系代词that,而用了the one?

Is this car the one that you bought last winter?
is ok too.

Is this the car
Is this car the one

(that) you bought last winter

you bought last winter是个定语从句，修饰前面的the one (car)其实也可以完整地说：
This car is the car that you bought last winter.
但考虑不重复罗嗦，就用one代替，是不能省略的，不然前面的主句就不完整了。而that在这里就可省略了，前面有one就完全可以了！

后面有限定you bought last winter，用the one 是特指

其实也可以用that,不过the one 表示特指,起强调作用.