I haven’t got a mobile phoneI think you should have . It’s useful for you.A. one

问题补充：

--- I haven’t got a mobile phone.

--- I think you should have . It’s useful for you.

A. one

B. this

C. that

D. it

答案：

(答案→)A. one

B. this

C. that

D. it

解析：考查冠词用法。One指代可数名词单数，表泛指。This指代即将要说的事情。That指代不可数名词或者可数名词单数，后面必须要有定语修饰。It指代上文出现的同一事物。句意：—我还没有手机。—我认为你一个有一只手机，对你来说，手机很有用。故本题指的是一只手机。故A正确。