▲have a cold 和 have colds 意思没什么区别，都指“感冒”，但从用法上看，两者有些区别：

1. have a cold 通常指一次感冒。如：

He had a cold and coughed a little. 他感冒了，有点咳嗽。

I have got a cold and I cannot smell. 我感冒了，闻不出味道。

My son has a cold and a temperature. 我儿子感冒了，发烧。

The teacher excused me from exercise because I had a cold. 我因为感冒，老师准许我不用做运动。

2. have colds 通常指多次感冒、多人的感冒、经常性的感冒等。如：

Do you often have colds? 你常常感冒吗?

I have bad colds every year. 我每年都患重感冒。

Most people have two or three colds a year. 大多数人一年患两三次感冒。

As is well known, more people have colds in wet weather. 众所周知，大多数人在雨天感冒。

We all had colds and couldn’t stop sniffing and sneezing. 我们都感冒了，一个劲地抽鼻子，打喷嚏。

▲但以上区别并不绝对，有时两者都可用（比如表泛指时，用不定冠词或用复数均可）。如：

A cold is a very common complaint. 感冒是一种常见病。

Colds are a very common complaint. 感冒是一种常见病。

People say it can cure colds, but I’m a bit of a sceptic. 人们说它能治感冒，我有些怀疑。

People say it can cure a cold, but I’m a bit of a sceptic. 人们说它能治感冒，我有些怀疑。

▲go for a walk 与 go for walks 的区别与以上区别类似。