Which one of the following steps would be included in the primary response in humoral immunity?
a. antigen binds to antibodies
b. cytotoxic t cells bind to infected body cells and destroy them
c. t cells activate cytotoxic t cells
d. a macrophage consumes a virus and displays antigens on its surface and signals t cells to divide.

7th grade question (easy) look at the diagram of the food web. the arrows mean eaten by. what would happen if the number of snakes went down? answer choices are in the image.

Which structure in the cardiovascular system connect arteries to veins?

Which of the following best describes the purpose of the parathyroid hormone? a. it decreases the blood calcium level and decreases blood phosphorus level. b. it decreases the blood calcium level and increases the blood phosphorus level. c. it increases the blood calcium level and increases blood phosphorus level. d. it increases the blood calcium level and decreases blood phosphorus level.