Final answer:
The correct answer is B. phase contrast light microscope, which allows for the observation of living cells and their organelles by enhancing phase differences to produce high-contrast images without the need for stains.
Step-by-step explanation:
The microscope used to observe living cells and organelles by contrasting phase differences so that some regions appear brighter is the B. phase contrast light microscope. A phase contrast light microscope is designed to enhance the contrast in transparent and colorless specimens without the need for staining. This type of microscope utilizes phase shifts in light that passes through a transparent specimen to produce high-contrast images of living cells and their organelles.
The phase contrast microscope is excellent for detailed examination of internal cell structures such as the nucleus, endoplasmic reticulum, and mitochondria in a non-invasive manner, allowing for observation of cells in their natural state. In contrast, electron microscopes, like the transmission electron microscope (TEM) or the scanning electron microscope (SEM), achieve higher resolution but cannot be used to view living specimens as their sample preparation processes kill the cells.