This is cyclic change because the population is consistently going up and back down.
C I think is the answer but idk
Tracheae to distribute oxygen
Answer is c just took the test
Cells, tree, digestive system, public transportation system, government systems, school systems, families, dog, forest, pond, prairie, communication systems, towns, insect, solar system, weather systems, bird, correctional system, squirrel, soil, etc.
