Comparison of the amino acid sequence of Cytochrome C from different species shows many variations. Most of these variations are found:
Most of the variations in amino acid sequence affect primary structure but not secondary and teiary structures which are functionally impoant. Aminoacids responsible for the secondary and teiary structures (loops, helix or strands) are preserved but the aminoacids that do not contribute to the formation of secondary and teiary structures are altered. These alterations are distributed randomly as they result from point mutations on the gene. So "randomly" is the single best answer of exclusion. Ref: Bioinformatics for Beginners By Mani and Vijayaraj, 1st Edition, Page 165
Randomly
Only in helical region
Only in strand l region
Mainly in loop regions