I believe that the correct answer would be : Different types of organisms have different numbers of chromosomes.
I hope that this helps you !
Seasons, because the earths axis is tilted we have seasons. without the tilt we would never have seasons.
20. The answer is 1 (Precambrian)
21. The answer is 4 (Pennsylvanian)
22. The answer is 2 (Bony Fishes, Dinosaurs, and Mammals)
23. The answer is 2 (Reptiles)