De ce in English:

It would take me too much time to explain to you why it's not going to work.

If you're tired, why don't you go to sleep? "Because if I go to sleep now I will wake up too early."

Why?

If you need some money, why don't you borrow some from your mother?

We learned why the French Revolution broke out.

Why is politics separating us, when we ourselves know who is good and who isn't?

If you don't mind my asking, why did you go out yesterday?

Why have the apes evolved more than other animals?

Instead of going back to the party, why don't we go to my place?

Nobody understood why the elephant suddenly turned on its owner.

Why do Americans eat turkey on Thanksgiving?

Tom got to work later than usual this morning. I wonder why.

He stayed awake all night wondering why the deal went wrong.

They asked me what my name was, where I came from, and why I had come.

How about playing catch? "Sure, why not?"