When is it appropriate to use vosotros?
Vosotros is used to address a group of two or more people directly in an informal setting. Only certain Spanish speaking countries use this however.
How does passive immunization give rise to protection from disease?
Passive immunization is immunization with antibodies from outside the body against a particular pathogen. This immunity is not long term however, and may only last a few days. For example, passive immunization is administered to a person who is already infected with rabies for instance, that way the person is receiving antibodies directly against rabies in order to fight the pathogen.
What are the main blood group systems in humans and what makes them different from one another?
In humans, the main blood group systems are the ABO system and the Rh system. The ABO system describes the type of blood a person has (A, B, AB, or O), while the Rh system differentiates the type of protein on the surface of the red blood cells. For example, a person with type A positive blood has the A antigen on the blood cells and the Rh antigen as well.