Question

what do white blood cells do?
play a key role in fighting off infections.
play a key role in in transporting carbon dioxide.
play a key role in in transporting glucose.
play a key role in fighting off blood clotting.
play a key role in in transporting hemoglobin.

Explanation:

White blood cells, also known as leukocytes, are an important part of the immune system. Their main function is to protect the body against infections. They can identify and destroy pathogens such as bacteria, viruses, and fungi. Transporting carbon dioxide is mainly the function of red blood cells (through a process involving hemoglobin). Transporting glucose is not a primary role of white blood cells. Blood clotting is mainly related to platelets. Transporting hemoglobin is also a function associated with red blood cells (hemoglobin is the protein in red blood cells that binds to oxygen and carbon dioxide).

Answer:

Play a key role in fighting off infections.