Short difficult what am I riddles for teens

I am only useful when I am full, yet I am always full of holes. What am I?

I am a fruit. Remove my first letter, it's a crime. Remove my first and last letter, it's a kind of music. What do you think am I?

What am I?

Poke your fingers in my eyes and I will open wide my jaws. Linen cloth, quills, or paper, I will devour them all. What am I?

I take what you receive and surrender it all by waving my flag. What am I?

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

I have keys but no locks. I have a space but no room. You can enter, but can't go outside. What am I?

What has one head, one foot and four legs?

Everyone has me but nobody can lose me. What am I?

I am alive without breath and cold as death. I am never thirsty but always drinking. What am I?