Best Riddles and Answers

Question: I fly and never rest. What am I?

Question: I have keys but no lock, you can enter but not leave what am I?

Question: What is yours, but only others can use it?

Question: Why did the nudist not like going to London?

Question: Half of those who read this riddle, I am your best friend.
I depend on you, but it's you I will defend.

What am I?