why blood group O can donate to all blood groups

A person with blood group O can donate blood to all other blood groups because in case of O blood group, no antigens are present on the surface of RBC's where as antibodies present in plasma are anti A & B. When blood from a person with O blood group is transferred to persons with other blood group like A, B or AB, no reaction between antigen and antibody called agglutination takes place in that person. Thus a person with O blood group can donate blood to all other blood groups.