What characteristics of organisms older than 540 million years ago makes fossils?

The observations of hooke and van leeuwenhoek documenting the existence of microscopic cells formed the basis of what important theory? a. the cell theory stating that all living things are composed of cellsb. the theory of spontaneous generation, which held that life forms could arise spontaneouslyc. the theory of chemotherapy, or use of antimicrobials to destroy pathogenic organismsd. the germ theory of disease and causative agents

Penelope studies how the structure and function of the nervous system is related to behavior. she is a psychologist

Why do we perceive objects as retaining their brightness under different lighting levels?