Which One of the Following Descriptions of Ethics in Research

Which one of the following descriptions of ethics in research is most accurate?

A) What can be considered ethical or unethical is generally very clear-cut and straightforward.
B) Even by abiding to the law, your actions can be unethical.
C) Although ethics training is highly recommended at all universities within the United States, only about half require it.
D) The ethical standards of scientific research on human subjects have not really changed in the last hundred years.