The basic functional unit of the human kidney is:

Kidneys of mammals are present on either side of the vertebral column at the level of:

The wall of the urinary bladder in humans shows a thick layer of smooth muscle called . . . . . . .

Identify the wrong statements about the human excretory system and choose the option accordingly.
$I.$ Kidneys are reddish-brown and bean-shaped structures.
$II.$ Kidneys are situated between the last thoracic and third lumbar vertebrae.
$III.$ Each kidney of an adult human measures $10-12 \, cm$ in length,$5-7 \, cm$ in width,$2-3 \, cm$ in thickness,and has an average weight of $120-170 \, g$.

The functional and structural unit of the kidney is ........ .

Provide definitions/explanations for the following terms:
$(1)$ Malpighian body
$(2)$ Sebaceous gland