Which of the following statements are correct about the principles of medical ethics?
选项：

A:The principles of medical ethics can be conflict with each other. ;
B:When two good options are available, the better one is preferred; when two bad options are available, the less worse one is preferred. ;
C:Sometimes, a treatment carried out for good intention may cause harm to patient. ;
D:In clinical research, it is abolutely necessary to disclose all the risks that are accoaited with the study to the participants.