Afamily can share a genetic risk of developing cancer if:
a. a germ-line mutation in one of the genes implicated in the cancer occurred in an ancestor.
b. the cancer is caused by somatic cell mutations.
c. a somatic cell mutation in one of the genes implicated in the cancer occurred in an ancestor.
d. all of these choices are correct. the cancer is caused by germ-line mutations.

The correct answer is A. a germ-line mutation in one of the genes implicated in the cancer occurred in an ancestor.

Explanation:

Somatic cells do not take part in gamete formation so these cells are not involved in the producing offsprings, therefore, any mutation in somatic cells in one of the genes implicated in cancer occurred in an ancestor will not pass to offsprings.

Mutation only can pass if it occurred in the germ cells because germ cells form male and female gametes that fuse with each other during fertilization and produce offspring. So germline mutation can pass from one generation to another generation.  So the right answer is A.