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(A) There is no doubt that the frogs’ hearing ability is still crucial to their survival.
(B) Closing the tubes improved the frogs’ ability to hear high frequencies and ultrasounds, while opening them increased sensitivity to low-frequency noises.
(C) Further studies of the amphibian’s hearing showed that its eardrums vibrate in response to ultrasonic noises, but only some of the time.
(D) In other words, the frogs’ tunable ears are an adaptation to their noisy home environments.