Which of the following collections of subsets of the plane, R2 , are partitions?
(a) {{(x; y) | x + y = c}| c  R}
(b) The set of all circles in R2
(c) The set of all circles in R2
centered at the origin together with the set {(0; 0)}
(d) {{(x; y)} | (x; y)  R
2
}