Milk?

CORRECT!
Level 1 riddle!

I belong to you,
Yet others use me the most.

What am I?

Air?

Name!

Correct!
Level 2!
Always on top,
White or transparent,
Powder or block,
Carving valleys and filling seas.

Ice.

Correct! 2 points for Cello!
Level 1 Joke from Torgi:
What can you catch but not throw?

A cold?

YOU GOT IT!

This is a level 3 riddle:

In a glass house by the beach reside strange brothers three,
As different as any three brother might be,
Yet try as you might to tell brother from brother,
And you’ll find that the trio resemble each other.
The first isn’t here, though he’ll come beyond doubt.
The second’s departed, so he’s not about.
The third and the smallest is right on the spot,
And manage without him the others could not.
For the third is a force with which to be reckoned, 
As he turns the first brother into the second.
So tell me, my child, are the three of them one?
Or are there but two, or could there be none?
Just name them, and you will at once realize
That each rules a kingdom of infinite size.
They rule them together, and are them as well,
In that, they’re alike, so where do they dwell?

Past, present and future?