The fact that astronomers have observed billions of stars clustered together is evidence that -- a. stars must have some sort of attraction for each other. b. all sections of space have the same numbers of stars. c. galaxies are probably older than the stars that make them up. d. the distance from one star to another varies, depending on the temperature of the star.

What re the two main phrases of the cell cycle.

Compare the depth of field when focusing with low power and high power. which power has the greater depth of field?

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.