Which of the Following Is Not a True Statement

Which of the following is not a true statement?

A) The results of an experiment can befluenced by either the expectations of the subject or those of the researcher.
B) The experimental method is the only one which can be used to identify cause-effect relationships between variables.
C) Properly conducted experiments are always free offluence of a researcher's expectations
D) Ethical considerations can sometimes prevent researchers from using the experimental method even when they want to learn about cause-effect relationships.