关于薄冰教授的这个说法：

1. a five-year-old boy 一个五岁的男孩

2. a four-months-long winter  一个长达四个月的冬天

前者year 用单数，后者months 用复数，既没说明原因，也无依据可考，百思不得其解。最后，只好借助于英美语料库。经查阅语料库CORPUS OF CONTEMPORARY AMERICAN ENGLISH，惊奇发现：long 表时间（不是长度）之前的名词不用复数。结果如下：

1. two-month-long：10个例句。

2. three-month-long：18个例句。

3. four-month-long：12个例句。

4. five-month-long：7个例句。

5. six-month-long：18个例句。

限于篇幅，仅举部分例句：

...which saw a failed coup attempt and a two-month-long national strike.

In 1999, a two-month-long war erupted between the two countries.

I'm about to attend a three-month-long birthday party where I can have my cake and eat it, too.

which is a small but crucial piece of a three-month-long program called Challenges and Possibilities.

The four-month-long trial was the second time...

What was coming was a four-month-long seminar in the art of losing.

After a five-month-long investigation, Christ Koulis is arrested and charged with murder.

That was the beginning of a five-month-long exchange of e-mails.

On the six-month-long trip over from Earth, she'd had a tryst with the pilot.

70 million people are expected to visit Shanghai during the six-month-long World Expo this year.

But I think the judge is clearly trying to save this six-month-long case from going down the tubes so quickly.

以下例句摘自国内外英文报刊和网络：

During his two-month-long excursion, Hayes visited 16 European countries. 在他2个月的远足中，Hayes游览了16个欧洲国家。

“Living Stories” was Google's “experimental format for displaying news coverage” a two-month-long experiment with the New York Times and Washington Post. “生活故事”是Google和《纽约时报》及《华盛顿邮报》合作的一个项目，该项目已持续2个月，目的是探索“展示新闻报道”的新方式。

The United Nations peacekeeping force in Lebanon says Israel has lifted it two-month-long sea blockade of the country. 在黎巴嫩的联合国维和部队说，以色列已经解除对黎巴嫩两个月的海上封锁。

The move could resolve a two-month-long political deadlock that has worsened Iraq's precarious security situation and contributed to an increase of sectarian killings across the nation. 这一举动打破了长达两个月之长的政治僵局，而此僵局曾一度使伊拉克不稳定的社会形势恶化，并导致了国内宗派屠杀数量的增加。

I would love to play in South America. I had such a good time there when I was a junior, playing many tournaments during a two-month-long trip. 我很想在南美比赛，当我是一个孩子的时候我在这里度过了美好的时光，在两个月长的旅行中我参加了很多比赛。

To understand Putonghua promotion in Yantai, we conducted a two-month-long survey of the community. 为了解普通话在烟台的推广情况，我们进行了一次历时两个月的社会调查。

The content of the movie is not certainly complex: In the crowd of special troops, two Chinese are left over four qualified students after three-month-long devil trainings. 这部影片的内容并不复杂：一群特种兵，两个中国人，三个月的魔鬼训练，剩下四个合格的学员。

However, this position frequently requires three-month-long trips abroad. Is that acceptable? 但是这职位，经常须要外派三个月左右，你能接受吗？

I have just been through with a three-month-long training. 我刚完成了一项为期三个月的训练。

But it's safe to say that he probably made a year's salary in the three-month-long marriage. 不过，保险地说，他大概至少从这三个月长的婚姻中赚得了一年的工资吧。

They said their airport protest was justified as part of their six-month-long campaign to remove an elected government they believe is a puppet of ousted leader Thaksin Shinawatra. 他们表示，机场抗议理由正当，这是长达6个月抗议活动的又一个片段，为的是将选举政府赶下台去，推翻这个他信的傀儡政府。

For Shanghai, this six-month-long festival, which is set to attract 70 million visitors, is the equivalent of the Olympics in Beijing: a chance to showcase itself to the world. 如同北京奥运会，上海世博会将是中国展现自己的一个重要机会。

Organizers are expecting 70 million visitors during the six-month-long Expo, mostly from neighboring provinces. 有关组织者预期在为期六个月的博览会期间有主要来自周边省份的七千万参观者。

【特别说明】 在同样语料库输入复数的“two-months-long, three-months-long, four-months-long, five-months-long, six-months-long”，结果一个例句也没有查到。

大量实例证明，a four-months-long winter（一个长达四个月的冬天），是一个值得商榷的表达，网友的质疑是有道理的！