Identify the sentence that correctly uses the word "as" when making a comparison.
A. The ancient Greek mathematician Eratosthenes realized that he could determine the circumference of the Earth using a mathematical formula that is as simple as any taught in a high school geometry course.
B. The ancient Greek mathematician Eratosthenes realized that he could determine the circumference of the Earth using a mathematical formula that is simple as any taught in a high school geometry course.
C. The ancient Greek mathematician Eratosthenes realized that he could determine the circumference of the Earth using a mathematical formula that is as simple as a high school geometry course.