Explanation: The immune system is a complex network of cells, tissues, and organs that work together to identify and respond to foreign substances in the body, including bacteria, viruses, parasites, and toxins. Its primary function is to protect the body from infections and other harmful substances.

Incorrect choices:

a. The regulation of body temperature and blood pressure is primarily controlled by the nervous and endocrine systems, not the immune system.

b. Digestion and absorption of nutrients from food are processes mainly controlled by the digestive system, not the immune system.

d. The production of hormones that control bodily functions is primarily the responsibility of the endocrine system, not the immune system.