Which of the following organs is NOT a part of the immune system? A)Appendix
B)Tonsils
C)Peyer's patch
D)Thymus

In addition to seeds, which of the following characteristics are unique to the seed-producing plants? a) sporopollenin b) lignin present in cell walls c) pollen d) use of air currents as a dispersal agent e) megaphylls

What are some characteristics of a free enterprise economy?

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