干吗的英文：
[Informal] why on earth; whatever for

参考例句：

Why not try the oyster stew?
干吗不试试炖牡蛎

Must your brother tag along with us everywhere we go
你兄弟干吗总紧跟着我们?

I can't make it out why should you get it out on the kids at the drop of a hat
我真不理解你干吗动不动就拿孩子们出气呢?

Why not come along?
你干吗不一起去?

Why did she have a tilt at him at the meeting?
她干吗在会上攻击他?

Must your brother tag along with us everywhere we go?
你兄弟干吗总紧跟着我们？

Would you like some waffles?
你想要一些华夫饼干吗？

What are you stretching your neck for?Can't you see well?
你干吗伸长脖子？你看不见吗?

I really do not know why they shall be shouting like this.
我真不知道他们干吗要这样大喊大叫。

Why the hell don't they stop shouting?
他们究竟干吗不停止叫喊？

informal是什么意思：
adj. 非正式的；口语体的，通俗的；不拘礼节的

Informed judgement.
有事实根据的判断。

This is an informal expression.
这是一种非正式表达法。

This is an informal word.
这是一种口语用语。

why是什么意思：
adv. （用作疑问副词）为什么，（用做关系副词）为什么
n. 原因，理由
int. 咦，哎呀，哦，当然，唔

Why are you in such a hurry?
你为什么这样急呢?

Is this why the Yen is so strong?
这是日元如此强劲的原因吗？

Why, I was fast asleep.
怎么，我睡得很熟的呀。

earth是什么意思：
n. 地球，世界，陆地，地面，土；兽穴
v. 把（电线）接地；埋入土中；躲入洞内

This is paradise on earth.
这是世上的极乐。

pit in the earth
地下的洞穴

to earth a body
埋葬一具尸体