An investigator wishes to watch the movement of
c. elegans (a roundworm). what type of microscope should she use?

If the investigator wishes to watch the movement of C. Elegans (a roundworm), then he should be using compound microscopes. These microscopes are light illuminates and image that can be perceived is a two dimensional. Using this would allow you to magnify to a certain level so you can view individual cells and even cells that are living and moving. Typically compound microscopes can magnify up to 1000 times magnification. It has two convex lenses which has short focal lengths to allow a much higher level of magnification as compared to a simple microscope. These lenses are called the ocular lens and the objective lens.

If its history of, then b) because a) implies only present day (now)