the least effective is definitely B. Since it is a complex situation as you say then written communication will not do at all and might make things worse if it caused misunderstanding which happens a lot in written communication.
Similarly, what is the only method of birth control that is 100 percent effective?
The chart on the following page compares how well different birth control methods work. The most effective way to prevent pregnancy is abstinence . However, within the first year of committing to abstinence, many couples become pregnant because they have sex anyway but don't use protection.
How effective is birth control pills?
Birth control is a way for men and women to prevent pregnancy. There are many different methods of birth control, including hormonal contraception such as "the pill." Women take the pill by mouth to prevent pregnancy, and, when taken correctly, it is up to 99.9% effective.