What Tree Is That?™ Mobile

Is there a single, small (1/8"-1/4" long) bud at the end of each twig?
CLUE: The fruit is 2-3 rounded nuts in a prickly bur.

Are there several, small (1/8"-1/4" long) buds at the end of each twig?
CLUE: The fruit is an acorn.

Are the buds 3/4"-1" long, with the fruit a bur enclosing 2-3 triangular nuts?
CLUE: The bark is thin and blue-gray.