The bones of forelimbs of whale, bat, cheetah and man are similar in structure, because:

The bones of forelimbs of whale, bat, cheetah and man are similar in structure but get developed into different direction to adapt to different needs. This is called as Divergent evolution. And these structures which are similar anatomically but perform different functions are known as Homologous structures. And homology shows these living organisms have common ancestor.

Hence the correct answer is option (b).