21 Consonants in the Alphabet
21 Percent Oxygen in (the) Atmosphere
ten commandments
4 Cardinal Points of the Compass
10 Centuries in a Millenium
7 C in the W = 7 Continents in the World.
This is a Ditloid. The answer is 0 (zero) Sides on a Circle.
100 counties in North Carolina
100 Runs in a Century
122 spaces in a Chinese checker board
4 g in a cc is a ditloid, a type of word puzzle, each letter in the ditloid is the beginning of a word , you have the work it out, in this case the answer is Four Ghosts in a Christmas Carol.
12 Picture cards in a deck
1973: Britain Enters the Common Market.