Most variations in aminoacid sequence of cytochrome c affect primary structure in a way not to affect the secondary and teiary structures which are more impoant for function.The amino acids that cannot be replaced without a major modification of the enzymic propeies of the cytochrome c are not altered.Thus the amino acids at locations that determine the secondary structure of protein (loops, helix or strands) are preserved while aminoacids that do not contribute to the determination of secondary and teiary structure are preferentially altered.These alterations are likely to be distributed randomly as they result from point mutations on the responsible gene and this is the single best answer of exclusion here.