Use the Following Information When Answering the Corresponding Questions)

Use the following information when answering the corresponding questions) .
Lymph hearts are pumping structures that drive lymph through the lymphatic system, returning it to the circulatory system a large veins entering the heart. Researchers examined rate and strength of pumping of lymph hearts in two species of amphibi toad Bufo marinus) and a frog Rana catesbiana) . During hemorrhage or dehydration, the volume of blood in the circulatory system falls. A hormone, arginine vasotocin AVT) , is released in these situations. The researchers examined the effect of AVT on lymph heart function. They found that AVT increased pressure at the lymph heart, but did not affect the rate of lymph heart pumping. They also examined the effect of atrial natriuretic peptide ANP) , a hormone that is released when blood volume is higher than normal. E. A. DeGrauw and S. S. Hillman. 2004. General function and endocrine control of the posterior lymph hearts in Bufo marinus and Rana catesbiana. Physiological and Biochemical Zoology 774) :594- 600.)
-Many organs have adaptations to increase the rate of diffusion of a gas or solute. How are fish gills adapted to optimize oxygen absorption?

A) Continual flow of water across the gills
B) Co- current flow of water across the gills and blood within the gill capillaries
C) Countercurrent flow of water across the gills and blood within the gill capillaries
D) Bidirectional flow of water across the gills