Good Riddles

Question: When you bend me I'm kind
But I'm very hard to find
I'm easily sold
and rhyme with this when told

What am I?

Question: When is a door not a door?

Question: What is only a small box but can weigh over a hundred pounds?

Question: I am the black child of a white father, a wingless bird, flying even to the clouds of heaven.
I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth I am dissolved into air.

What am I?

Question: Hold me by the neck and I won't mind,
if I get wrong I just need a good wind.
If you want me you better pick wisely,
just use your ears and I'll follow you blindly.

What am I?