What force and strength cannot get through, I with my unique teeth can do. What am I?

Answer: A Key

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What gets sharper the more you use it?
What never asks questions but is always answered. What am I?
What’s strong forever, Never broken. Forged from fire, But never smoking. It’s true value, Not a must. Man for man, We kill in lust. What am I?
When filled I can point the way. But when empty unmoving I stay. What am I?
When I am sad, I change colour from white to grey. My tears fall to the ground and my cries are low and rumbling. In my anger I send great flashes of light above. What am I?
When I point up it's bright, but when I point down it's dark. What am I?
When I point up, it’s bright. When I point down, it’s dark. What am I?
When I take five and add six, I get eleven, but when I take six and add seven, I get one. What am I?
When I’m first said, I’m quite mysterious, but when I’m explained, I’m nothing serious. What am I?
When it comes to me, you go on red and stops on green. What am I?
When people can control me, people love me. When people lose control of me, people fear me. I cast shadows, but have no shadow myself. What am I?
When set loose, I fly away. Never so cursed, as when I go astray. What am I?