When crossing over occurs, all the alleles below the position of the chiasma are exchanged. The homologous parent chromosomes are shown on the left (before the first arrow). As a result of crossing over, two allele changes occurred between non-sister chromatids to produce a new arrangement of alleles (see yellow highlights). The alleles that were exchanged were c with C and d with D, so the crossover event producing this combination must have been a result of chiasma between genes B and C (Statement II).
If chiasma formation had occurred between genes A and B, the alleles for all three genes, B, C and D, would have been swapped (Statement I). If chiasma formation had occurred between genes C and D, then just the alleles for gene D would have been swapped (Statement III).
