The right answer is A patient who is Rh– can receive only Rh– blood.
The blood group is not the only thing that matters, it adds a category: rhesus. Rhesus refers to a red blood cell antigen that is on their wall. There are two blood group systems: Rh positive (Rh +) and Rh negative (Rh-).
Rhesus is positive in people who have this antigen. It concerns the majority of the population. Negative rhesus refers to people without the antigen. This rhesus factor is especially useful to know if a blood transfusion is feasible between two people.
The blood transfusions can be "iso-rhesus", that is to say between Rh + and Rh- but only in one sense: Rh- can give to Rh + but Rh + can not give to Rh-. Again because of the presence of antibodies directed against the antigen in Rh- people.
Yes it is important to know a person's Rh factor, but you can give an Rh+ patient Rh- blood only once because after that their body will build a defense mechanism against it and the blood will be rejected the second time.
