Why Does Inheriting a Mutation in a Gene Increase One's

Why does inheriting a mutation in a gene increase one's risk of developing cancer?

A) It takes more than one mutation to develop cancer.People who inherit a mutation need fewer additional mutations to develop cancer.
B) It takes one mutation to develop cancer.People who inherit a mutation are already developing cancer as soon as they are born.
C) It takes one mutation in the right gene to develop cancer,so if they inherit a mutation in a key gene,then they will develop cancer.
D) Inheriting a mutation means we don't need mutations from outside sources to develop cancer.
E) None of the above.