NoBlood

Ok i know i've asked something similar to this before and the advice is always :"Do your research." Well, i've done my research, but i still don't think i understand this.
Alot of doctors are giving me the impression that the C selection of my advanced health care directive will leave me kind of unprotected since it means that a doctor will have to discuss treatment options with me or my health care agents before treating me. However, in my mind by selecting the B option it looks to me like i might be limiting myself since there is no way for me to know and/or actually state all the minor fractions that i may be willing to accept. So what do i put down? Am i miss reading something or just making this more complicated then it really is?
Lupin