Answer:
What is the smallest sentence with all letters in the English alphabets?
Upon me you can tread, though softly under cover. And I will take you places, that you have yet to discover. I'm high, and I'm low, though flat in the middle. And though a joy to the children, adults think of me little.
I am a box that holds keys without locks, yet they can unlock your soul.
Hold these between your knees if you want to set a Cuban beat.
What has roots that nobody sees, and is taller than trees. Up, up it goes, and yet it never grows.
You use it between your head and your toes, the more it works the thinner it grows.