Professor: Well, turns out dolphins have a structure in their foreheads, just in front of their nasal sacs, called a melon. Now, the melon is kind of a large sac-like pouch, made up of fat tissue. 根据教授所说，melon 位于海豚前额的鼻囊里，由脂肪组织构成的。后文又说这种组织可以帮助海豚发射声波。B 选项正确。