Final answer:
To observe tissues under a TEM, thin sections of the tissue are cut and stained for contrast, as the TEM uses a beam of electrons for higher magnification and resolution.
Step-by-step explanation:
To view tissues under a transmission electron microscope (TEM), the correct method is by cutting thin sections of the tissues and observing them under the microscope. This is because electron microscopes require specimens to be extremely thin so electrons can pass through them for imaging. Additionally, TEM uses a beam of electrons and operates in a vacuum, which means the tissue must be fixed and dehydrated, making it impossible to view living specimens. Tissue sections are often stained with heavy metals that scatter electrons, providing contrast to the image. Unlike a brightfield microscope or a darkfield microscope, which utilize light to view specimens, the TEM provides higher magnification and resolution by using electrons.