SAT Subject Biology Practice Question 197: Answer and Explanation
7. Which of the following uses a countercurrent exchange system?
A. I and III only
B. II and IV only
C. I, II, and III
D. I, II, and IV
E. I, II, III, and IV
Correct Answer: D
Gills, kidneys, and lungs all rely on countercurrent exchange for the intake of oxygen and/or release of waste compounds. The intestines do not feature countercurrent exchange.