Which Statement About the Structure of the Fish Gill Is

Which statement about the structure of the fish gill is true?

A) Efferent vessels bring blood to the gills, whereas afferent vessels take blood away from the gills.
B) Exchange of respiratory gases occurs within the lamellae of the gill filaments.
C) The efferent and afferent vessels are the countercurrent flow system of the gill.
D) The lamellae are further subdivided into gill filaments.
E) The opercular flaps open to take in water from outside into the gill chamber.