Sperm whales can produce stronger ultrasonic waves to kill their prey than dolphins.

C
解析：问题中的关键词是kill，本题说鲸鱼能发出比海豚更强烈的超声波去杀死猎物。利用信息词Sperm whales，ultrasonic waves和prey作为答案线索，对应原文第五段，“They do a whole range of other sounds like barks．groans and a kind of gunshot．”he said．“The gunshot is an intense pulse of sound．Sperm whales use it to stun their prey．”原文说鲸鱼会发出高脉冲声波恐吓猎物，未提及杀死猎物的内容，因此选C。