The indented area of the lymph node where efferent lymphatic vessels exit is called the

A. Tracheobronchial nodes are located near the trachea and bronchi in the chest and drain lymph from the lungs and airways, not from the arm or breast.
B. Axillary nodes are located in the armpit (axilla) and drain lymph from the arm, breast, and upper chest. They are a key part of the lymphatic system for these regions.
C. Inguinal nodes are located in the groin and drain lymph from the lower limbs, external genitalia, and lower abdomen.
D. Cervical nodes are located in the neck and drain lymph from the head and neck region, not from the arm or breast.

A. None of the answers are correct is incorrect because one of the options does result in active immunity.
B. Antiserum administration involves the transfer of antibodies (passive immunity), not the activation of the immune system to produce its own antibodies.
C. Vaccination induces active immunity by stimulating the immune system to produce its own antibodies and memory cells in response to a weakened or inactivated pathogen (or its components). This prepares the body for future exposure to the actual pathogen.
D. Breast feeding provides passive immunity because the infant receives pre-formed antibodies from the mother through breast milk, but does not stimulate the infant's immune system to produce its own.