Best riddles

It is impossible to keep it until you give it someone else. What is that?

Which month has 30 days?

What did the baseball glove say to the baseball?

Something very extraordinary happened on the 6th of May, 1978 at thirty-four minutes past twelve a.m. What was it?

I build up castles. I tear down mountains. I make some men blind, I help others to see. What am I?

What happens when you slap Dwayne Johnson's butt?

A hungry donkey was tied to a rope eight feet long. About thirty feet away there was a basket of fresh carrots. The donkey wanted to eat those carrots. How did he reach them?

A farmer is travelling with a fox, a sheep and a small sack of hay. He comes to a river with a small boat in it. The boat can only support the farmer and one other animal/item. If the farmer leaves the fox alone with the sheep, the fox will eat the sheep. And if the farmer leaves the sheep alone with the hay, the sheep will eat the hay. How can the farmer get all three as well as himself safely across the river?

What do you get when you cross a fly, a car, and a dog?

What is so delicate that saying its name breaks it?