Answer:
Without this, H2O would just be 2O
What occurs four times in every week, twice in every month, only once in a year but never in a day?
What can go up but never come down?
He's small but he can climb a tower.
I am your mother's brother's only brother in law. Who am I?
All about, but cannot be seen, Can be captured, cannot be held, No throat, but can be heard. Who am I?