29. Clonal selection
(A) determines the pool of mature leukocytes that will be stimulated by macrophages.
(B) requires the activation of natural killer cells.
(C) describes the proliferation of B and T lymphocytes after they have been activated by an antigen.
(D) requires the presence and activation of complement.
(E) describes the selection of mature non-self T cells.

25. In mammals, blood returning from the head will pass through the ________ just before entering the right atrium. (A) left atrium (B) superior vena cava (C) inferior vena cava (D) aorta (E) right atrium

26. During ventricular systole, the semilunar valves ________ and the AV valves ________. (A) open； open (B) close； open (C) open； close (D) close； close (E) open, unchanged.

27. Which of the following cells are phagocytes? (A) monocytes and neutrophils (B) basophils and eosinophils (C) eosinophils and lymphocytes (D) lymphocytes and basophils (E) monocytes and mast cells

28. Which is the correct order of steps taken by B and T cells to defend against infection in body fluids and cells? 1. B and T cells move to the lymph nodes, spleen, and other parts of the lymphatic system. 2. B and T cells leave the bone marrow and thymus and move to the bloodstream. 3. B and T cells meet and begin to fight viruses or other infectious agents. 4. B and T cells develop antigen receptors.(A) 4, 2, 3, 1 (B) 2, 4, 3, 1 (C) 4, 3, 2, 1 (D) 2, 4, 1, 3 (E) 4, 2, 1, 3

30. Complement proteins can do all of these functions except (A) enhance phagocytosis by innate immune cells by attaching to cell invaders. (B) help trigger the inflammatory response. (C) attack cancer and virus-infected cells after they are released by natural killer cells. (D) act as chemical signals to recruit more immune cells to the site of infection. (E) lysis of target cells.

31. What is passive immunity dependent upon? (A) a person's own immune system producing antibodies (B) antibodies made by another organism (C) antibody-producing cells from another organism (D) antigens from a person's own body (E) antigen stimulates antibody production

32. What is the advantage of excreting nitrogenous waste in the form of ammonia? (A) Ammonia is less toxic than uric acid. (B) Ammonia is less soluble than uric acid. (C) Ammonia excretion conserves energy. (D) Ammonia does not diffuse across cell membranes. (E) Ammonia excretion expends energy.

33. Which option correctly lists the structures in the kidney in the order in which fluid flows through them? (A) proximal tubule, Bowman's capsule, loop of Henle, distal tubule, glomerulus (B) Bowman's capsule, proximal tubule, loop of Henle, distal tubule, glomerulus (C) glomerulus, Bowman's capsule, loop of Henle, proximal tubule, distal tubule (D) glomerulus, proximal tubule, distal tubule, Bowman's capsule, loop of Henle (E) glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule

34. Where along the nephron is glucose reabsorbed from the filtrate back into the blood? (A) distal tubule (B) loop of Henle (C) proximal tubule (D) Bowman's capsule (E) renal pelvis

35. What is the function of antidiuretic hormone? (A) to increase urination (B) to increase water reabsorption (C) to stimulate sodium reabsorption (D) to counter the effects of alcohol consumption (E) to reduce water reabsorption