Which blood type could be given as a transfusion for patient with ab blood when the rh factor is unknown?
a. o+
b. a+
c. ab+
d. ab–

Patient with blood type AB RH+ can receive any type of blood, but patient with blood type AB RH- can receive all type of blood which also have RH- factor.

So here if we don't know the RH factor then the safest option is to give this patient AB RH-.

But if we would know that patient have RH+ factor then he can receive any blood type no matter what is the RH factor or blood type.

So correct answer is D. AB RH-