Final answer:
The compound operating microscopes use laser-induced refraction for variable magnification of tissue, which can be quite intense and must not degrade the specimen.
So, the correct answer is D) Laser-induced refraction.
Step-by-step explanation:
When using a microscope, we rely on gathering light to form an image. Hence most specimens need to be illuminated, particularly at higher magnifications, when observing details that are so small that they reflect only small amounts of light. To make such objects easily visible, the intensity of light falling on them needs to be increased.
Special illuminating systems called condensers are used for this purpose. The type of condenser that is suitable for an application depends on how the specimen is examined, whether by transmission, scattering or reflecting.
So, the correct answer is D) Laser-induced refraction.