I need help in these questions Please answer them correctly and 100%. I have only 20 minutes. Please do them correctly

Question 27 has occurred. When the comparison group is in some way affected by, or affects, the treatment group, regression effect endogenous change external effect contamination Question 28 Which of the following is not a current ethical standard concerning the treatment of human subjects? O A. Research should cause no more than a minimal risk of harm to subjects. OB. Confidentiality must be maintained unless explicitly waived. Oc. Subjects should be compensated for their time and effort. OD. Researchers should fully disclose purposes of research