举个例子说,i want to eat the third applei want to eat a third applethe的用法是特指,所以此句中特指的第三个苹果,大家都知道是哪一个,可能是摆在桌子上之类的a是泛指,此句中是指我要吃第三个苹果,是我吃了两个之...