Which gas is most abundant in the atmosphere?

a.
argon

b.
oxygen

c.
nitrogen

d.
carbon dioxide

The vaccine in a flu shot contains weakened flu viruses. how does a flu shot work with the immune system? a. it destroys lymphocytes. b. it destroys macrophages. c. it activates macrophages. d. it activates lymphocytes.

Which of the following is the earliest era of earth's geologic time scale? cenozoic mesozoic precambrian paleozoic

Male satin bowerbirds build bowers like the one shown below. they decorate the bowers with brightly colored blue objects in order to attract females. male bower birds attract mates with their a. feathers b. looks c. behavior d. songs