Leukemia is a form of cancer that affects a. lymphatic tissue. b. bone tissue. c. blood-forming cells. d. nervous system structures.

Leukemia is a type of cancer that originates in blood or bone marrow, and affects the body's ability to produce healthy blood cells. Generally, it affects the white blood cells, which are responsible for fighting infections and other diseases within the body.

Now that we know leukemia affects the blood cells, let's analyze each answer choice to find the correct one: a. lymphatic tissue: Lymphatic tissue is part of the immune system and is responsible for filtering lymph, which is a fluid that carries white blood cells. Despite being an essential part of the immune system, it's not the primary site where leukemia originates. b. bone tissue: Bone tissue is responsible for providing support, protection, and movement to the body. Although bone marrow (found within bones) plays a significant role in blood production, leukemia specifically targets blood-forming cells, not the bone tissue itself. c. blood-forming cells: Blood-forming cells, also known as hematopoietic stem cells, are responsible for the production of all types of blood cells - red blood cells, white blood cells, and platelets. Leukemia affects these cells, causing them to malfunction and produce unhealthy blood cells in excessive amounts. d. nervous system structures: The nervous system structures, including the brain and spinal cord, play essential roles in transmitting information and controlling various body functions. While some types of cancers can affect the nervous system, leukemia is not one of them.

Based on our analysis and understanding of leukemia, the correct answer is: c. blood-forming cells.