Good Riddles

Question: I have two arms, but fingers I have none. I've got two feet, but I cannot run. I carry well, but I carry best with my feet off the ground. What am I?

Question: When you do not know what I am, then I am something. But when you know what I am, then I am nothing. What am I?

Question: There are five people at a table and a pie sliced into 5 pieces. Each person has a piece of pie in front of them, yet the pie tin still has a piece of pie in it. How is this possible?

Question: What is the only question you can't answer yes to?

Question: How can "L" be greater in size than "XL"?