Which of the Following Statements Supports the Hypothesis That the Bidirectional

Multiple Choice

Which of the following statements supports the hypothesis that the bidirectional gas flow occurring in humans air goes in and out through the same passages) is less efficient than the unidirectional flow in fish?

A) Bidirectional flow in humans does not take advantage of countercurrent exchange.
B) About one- third of the air in human lungs is trapped in "dead space" where gas exchange with the circulation cannot occur.
C) None of the above are true.
D) Both A and B are true.