Which of the following are primary lymphoid organs?
a. bone marrow and thymus
b. appendix and spleen
c. lymph nodes and tonsils
d. spleen and thymus

a.bone marrow and thymus

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs

a=c and then d= c because of the band so you get ac/dc and you add them together you get sound waves