Genetic counselors work mostly a. school counselors. b. researchers in genetic engineering. c. elderly adults who live in care facilities. d. couples who are planning to have children.

Ans. (D) couples who are planning to have children.

Genetic counselors are healthcare experts, who advise peoples and families having risk of genetic disorders or are affected by genetic diseases to guide them about psychological, medical, and familial implications of factors for the disease.

Generally, they work with couples who are planning to be parents as they perform genetic testing. They provide information about risk of genetic disorders in their children, if there is close family member affected or with risk of genetic disease.  

Thus, the correct answer is option (D).