1. Mike injured his knee while playing. Examination revealed that the injured area was red, swollen, and warmer than the surrounding area. What does this condition indicate?
   
   

an inflammation


a tumor–like growth


a hemorrhage

1. When a virus invades the body, some B cells recognize it as nonself and produce plasma cells that release a substance to kill the virus. What is this substance called?
   
   

antigen


antibody


pathogen

1. Which of the following forms blood clots?
   
   

fibrin


macrophages


thrombin

1. An antigen has invaded a mammal's body. Specific immune cells engulf and ingest it. Some of the digested pieces are displayed on the cells' bodies. What happens next?
   
   

B cells are activated and release antibodies.


T cells are activated and produce clones.


B cells withdraw the immune response as the antigen is killed.