Good Riddles

Question: I am a cave full of bones,
and the house of a worm.

What am I?

Question: No matter how hard you try,
I can open what you can't.
If it wasn't for me,
on your front porch you would stand.

What am I?

Question: What can you hear but not see?

Question: There are 57 ducks walking to a pond. On the way, 15 get lost, 26 head back, and 16 make it to the pond.

What happened to the rest?

Question: What temperature is twice as hot as 0 degrees Celsius?