"他的弟弟哭了" 的英文表达方式有很多种，以下是几种常见的表达方式：

His younger brother is crying.
His younger brother has been crying.
His younger brother was crying.

这些表达方式的来源都是英语的基本语法，是英语句子的构成部分。其中，"is/has been" 是助动词，表示正在进行或已经完成的动作。"was" 是过去式，表示过去的动作。

下面是一些具体的例句，以及中文翻译：

I saw his younger brother crying in the corner.
我看见他的弟弟在角落里哭。
His younger brother has been crying for hours.
他的弟弟已经哭了几个小时了。
I asked him why his younger brother was crying.
我问他为什么他的弟弟在哭。