Human blood is typed Rh⁺ (positive blood) or Rh^- (negative blood). This Rh factor is called an antigen. There are two other antigens known as A and B types. Blood lacking both A and B types is called type O. Sketch a Venn diagram showing the three types of antigens A, B, and Rh, and label each of the eight regions. For example, O1 is inside the Rh set (anything in Rh is positive) but outside both A and B. On the other hand, O2 is that region outside all three circles.