Human blood is classified by blood type, which indicates the presence or absence of the antigens A, B, and Rh, as follows.

A present Type A

B present Type B

Both A and B present Type AB

Neither A nor B present Type O

Each of these types is combined with a + or - sign to indicate whether the Rh antigen is present. Write a sample space containing all possible blood types. Do you think this is an equiprobable sample space? Explain.