one ¹

数词 one 一般跟可数名词连用或者受 of 短语限制：

one boy/pen/book/woman/girl/friend

one of the pens/books/women/girls/friends

或者用在下列短语中：

one ... the other, one ... another

你所提问的句子中的 one 完全是另一种词: 起替代作用的不定代词。它代替前面出现过的名词, 以避免重复。如替代的名词为复数, 则用复数形式的替代词 ones:

1. I haven't a pen. Can you lend me one? 我没有带钢笔,你能借给我一支吗? (one = a pen)

2. ‘Which shirt do you prefer?’ ‘This one.’ “您喜欢哪件衬衫?” “这一件。”

3. “I’d like two sweaters for my daughters.” “Certainly. The woolen ones are hanging here and the cotton ones are hanging there. Which would you like?” “我想给女儿买两件针织衫。”“好的。这儿挂着的是羊毛衫，那儿挂着的是棉针织衫。您喜欢哪一种？”

4. I didn't buy a calculator. They only had expensive ones. 我没有买计算器。他们只有贵的。

5. All the other boys have geography books and they will be ahead of me if I don't get one. 别的男孩都有地理书,如果我弄不到一本,他们就会超过我。

附注英语教师应注意,上面所说的“one 替代的是带不定冠词的名词”,并不是指在它前面出现的名词一定带有不定冠词,而是指它本身所在的位置上所替代的那个名词一定是带不定冠词的名词(无定的名词)例如:

The clean towels are in the drawer — if you need one. (one 实际上替代的是 a clean towel)

(2) 当 one 带有定冠词时 (the one)，它所替代的就是带定冠词的名词 (有定的名词) 了 (见 one $^{8}$ ):

The Endeavour was not a warship but an old merchant ship, just like the one on which Cook had learnt his seamanship. “奋力”号并不是一艘战舰，而是一艘旧商船，就像库克过去学航海技术时乘过的那艘船一样。(the one = the old merchant ship)

要注意,当 one 带有修饰语时,应带冠词:

1. We would be happy to sell it to you for 3,500 yuan, that is $50\%$ of the cost of a new one. 我们愿意以3,500元的价格出售给您，这个价格仅是一台新机的 $50\%$ 。

2. “Are you sure that there are no pages missing, and that it is just like the others, only second hand?” “Yes, it's as good as the new ones.” “您能肯定这一本没有缺页，和其它的书一样，只不过是二手货吗？”“是的，它和那些新书一模一样。”