#### Answer

Option (C)

#### Work Step by Step

The numbers $1, 2, 3, ...$ are positive integers.
If the number 0 in included, then:
The numbers 0, 1, 2, 3 are the nonnegative integers, for while 0 is not positive, it is also not negative.
Thus, the given set is the set of nonnegative integers.
The answer is Option (C).