Answers

2014-09-16T18:46:27+08:00
Blood type O (letter D) is known as the universal donor.
0
2014-09-16T21:03:43+08:00
The types of blood is also classified by "rhesus/ Rh". It refers to your blood if it has antigen or none. If it has antigen, it is called as Rh+. If none it is Rh - . 

Blood type o- is considered as the universal blood because they can give it to people having different blood types without risking a transfusion reaction.
0