Answer: The correct answer for the fill in the blank is A) Circulatory, immune.
Circulatory system also called cardiovascular system is a vast network of organs and vessels that allow the circulation of blood so as to transport nutrients, oxygen, other gases, and hormones to different parts of the body.
Blood contains different cells like white blood cells, red blood cells, platelets.
White blood cells ( also called leukocytes) work closely with immune system. They provide defense against pathogen ( disease causing organisms) through various ways ( like ingesting foreign material, producing antibodies to clear the antigens). By doing so, they protect us from infection and disease.
