Answer:
Without this, H2O would just be 2O
What has four fingers and a thumb but is not alive?
I am always hungry, I must always be fed. The finger I lick will soon turn red.
Something you carry while singing.
I'm the source of all emotion, but I'm caged in a white prison.
As round as an apple. As deep as a cup. All the king's horses can't pull it up.
Easy
Animal
Difficult
Food
Funny
Kids
Logic
What am I?