Which of the following scenarios refutes the argument that genes are entirely internally influenced?

a. patrick possesses a gene for brown hair, but his children have blond hair.
b. cindy possesses a gene for freckles, but she uses makeup to cover them up.
c. margaret possesses a gene for melanoma, so she chooses to stay out of the sun.
d. charles possesses a gene for alzheimer's, but he has not yet experienced symptoms.