Modular Arithmetic, Chinese Remainder Theorem, and Factoring - Lecture 20 (Discrete Math)

In the course's convention, what does Z sub n refer to?

1. A.The integers from 1 up to and including n itself
2. B.The first n elements of the natural numbers, 0 to n-1
3. C.Every integer whose absolute value is less than n
4. D.All multiples of n inside the natural numbers