Daniel is learning about how animals are classified into kingdoms and phyla. He is surprised to learn that living things were classified into two kingdoms, Animalia and Plantae, until the early 1900s. Where did scientists obtain the knowledge that they used to establish additional kingdoms?
A.
a wide variety of genetic and field investigations around the world
B.
experiments conducted after the invention of the microscope
C.
research conducted only in outer space
D.
research conducted mainly on genetic inheritance and clones