What is the most common infectious disease in the united states?
a. the common cold
c. pneumonia
b. the flu
d. strep throat

Which of the following birds remained ancient looking in the miocene epoch? a. crows b. owls c. grouses d. none of the above

Which statement best describes a keystone species? o a. it has littlelmenetic variation. it has an extremely high population. 0 b. 0 c. it remains unaffected by all environmental changes. od. it has a strong influence on the ecosystem. 0 e. it's the first species to populate a new ecosystem.

How can antibodies "remember" a particular bacterial invader or "antigen" on that invader?