Answer:
C. Kidney
Explanation:
Kidneys are not examined under the microscope because it is big enough to be seen with naked eyes. Their abnormal functionality can be observed physically or through other techniques like X rays, Ultrasound etc.
Other structures like pituitary gland, adrenal gland, pancreas and thyroid gland are also visible with our naked eyes however to examine their secretions it is the requirement of the laboratory to examine these structures under the microscope.