Another name for "mercy killing" is

euthanasia

Explanation: Assisted in taking your own life, in which the patient takes actions to terminate his or her life using means supplied by someone else, is different from euthanasia, in which a person takes an action that causes the death of another person. Euthanasia is sometimes called “mercy killing.”

Euthanasia is illegal in the United States. As of 2014, Belgium, Luxembourg, and the Netherlands permit euthanasia under very narrow circumstances involving competent patients suffering from painful terminal illnesses.

i beleive a. is the only possible answer