Which do you think a type of skin cancer called melanoma is, A or B?
The answer is A.
If there is an black mole-like-spot on the bottom of the feet which size is about a seed of watermelon, the outline is unclear and there is light and shade area of color, it can be skin cancer called Melanoma which is the most dangerous type of skin cancer.
Also if it is melanoma, the mole you got becomes bigger before you noticed. If there is no change in size, the possibility of melanoma is low.