(2) If E is urinary system, D is urine. The formation of urine has undergone two continuous physiological processes: filtration of the inner wall of glomerulus and renal capsule and reabsorption of renal tubules.

(3) Substance A is carbon dioxide, which is produced in human tissues and cells F, so the concentration of carbon dioxide is the highest at F. 。

(4) The liquid in circulation system B is blood, and the reason why blood is red is because it contains a red iron protein, namely hemoglobin, which is easy to combine with oxygen in places with high oxygen content; Where the oxygen content is low, it is easy to separate from oxygen; This characteristic of hemoglobin enables red blood cells to transport oxygen. When the number of red blood cells in blood is too small, or the content of hemoglobin in red blood cells is too low, people will suffer from anemia. People with anemia should eat more foods rich in protein and iron.

So the answer is: (1) ab; lung

(2) filtration of glomerulus and renal capsule; Renal tubular reabsorption

(3)F

(4) containing iron