'Happen' in the Bible

Mary asked the angel, "How can this happen, since I have not had relations with a man?"

Then Mary said, "Truly I am the Lord's servant. Let everything you have said happen to me." Then the angel left her.

Why should this happen to me, to have the mother of my Lord visit me?

He will come and destroy those farmers and give the vineyard to others." Those who heard him said, "That must never happen!"

And if they do this when the wood is green, what will happen when it is dry?"