In this image we can see that A is identical to B, and C is identical to D.
Chromatid (Cht) is a DNA molecule (the nucleofilament) associated with histone proteins (PH) and non-histone proteins (PNH)
Each chromosome of a cell may consist of one or two chromatids depending on its state: just after a mitosis, or after the second meiotic division, each chromosome consists of only one chromatid, the rest of the time, after DNA replication, each chromosome consists of two completely identical chromatids, connected by the centromere, thus giving the two rods the shape of an X.