Why is type O blood called the universal donor?

A) Because everyone with type O blood is Rh-, and therefore, this blood type cannot initiate any transfusion reactions
B) Because type O blood plasma does not contain anti-A or anti-B antibodies, so it can be transfused into recipients of any blood type
C) Because everyone with type O blood is Rh+, like most of the population, so this blood type is compatible with all others
D) Because type O red blood cells contain neither antigen A nor antigen B, so they can be transfused into most recipients of any blood type, without being attacked by antibodies
E) It is not well understood why type O blood can be transfused into people with all blood types.

Lymphocytes with a CD8 glycoprotein on their surface are called ________ cells and lymphocytes with a CD4 glycoprotein on their surface are called ________ cells.

A) cytotoxic T; B
B) B; cytotoxic T
C) B; helper T
D) helper T; cytotoxic T
E) cytotoxic T; helper