Reduced residue of n
Trivia · proposed by @vipproaccout
Which of the following is not a property of a reduced residue system modulo $n$?
AIt has exactly $n$ elements.
BNo two elements of the system are congruent modulo $n$.
CEvery element of the system is coprime to $n$.
DMultiplying every element of the system by an integer coprime to $n$ produces another reduced residue system modulo $n$.