As microscope technology improved over time, the magnification became advanced enough to discover cells in the 17th century. This discovery is largely attributed to Robert Hooke and began the scientific study of cells, also known as cell biology. Over a century later, the debate continued among scientists about how cells began. Most of these debates involved the nature of cell reproduction and the idea of cells as a fundamental unit of life. Cell theory was eventually formulated in 1839.

The three tenets to the cell theory are as described below:
1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of structure and organization in organisms.
3. Cells arise from pre-existing cells.
Anton van Leeuwenhoek is a scientist who saw cells soon after Hooke did. He made use of a microscope containing improved lenses that could magnify objects almost 30ox. Under these microscopes, Leeuwenhoek found moving objects that he named “animalcules,” which included protozoa and other unicellular organisms, like bacteria. He was also able to observe red blood cells and sperm cells. Leeuwenhoek's research can be used to support which of the tenets of cell theory?
A) Some cells emerge spontaneously.
B) Cells arise from pre-existing cells.
C) All living organisms are composed of one or more cells.
D) The cell is the basic unit of structure and organization in organisms.