Which of the following are complete residue systems modulo $11$? Which of the following are complete residue systems modulo 11?

$(a)\quad  0,1,2,4,8,16,32,64,128,256,512$

$(b)\quad  1,3,5,7,9,11,13,15,17,19,21$

$(c)\quad  2,4,6,8,10,12,14,16,17,20,22$

$(d)\quad  -5,-4,-3,-2,-1,0,1,2,3,4,5$

I have the answer which is that they are all complete residue systems modulo 11. However, I do not fully understand the definition of residue system or how to determine what sets make up a complete residue system?
To be a complete residue system modulo $n$, you need a set of $n$ integers, no two of which are congruent modulo $n$.
The correct answer is (b). 1, 3, 5, 7, and 9 are in their own remainder classes mod 11 while 11 is in cl(0), 13 in cl(2), 15 in cl(4), 17 in cl(6) 19 in cl(8), and 21 in cl(10). We have members of every remainder class  listed hence a complete residue system. The key is to know that all we need for a complete residue  system are members of every remainder class. Thomas defines a complete residue class as a set $S=\{r,s,\dotsc\}$ such that for every integer $k$ there exists a member of $S$, call it $m$, such that $k$ is congruent to $m$ mod $n$ or in the problem at hand mod 11. The complete residue system partitions the set of integers. It's important to realize that complete residue systems are not unique. All that's needed is that the set (the complete residue class) include any member of every remainder class.