Concept:White blood cells form the body’s defence system against infections and foreign invaders.
Explanation:White blood cells protect the body by fighting disease-causing organisms.
Some white blood cells produce antibodies that destroy pathogens.
Other white blood cells engulf and digest harmful microorganisms.
They do not produce haemoglobin or digestive enzymes.
They also do not mainly clot blood — that is the role of platelets.
Therefore, the correct option is the one describing production of antibodies and defence against infection.
Answer:C. produce antibodies to engulf disease-causing organisms.