听力原文： The rattlesnake, often considered the deadliest of all North American snakes, has often been the subject of research and discussion among naturalists. This snake earns its name from the presence of rings of tough skin on its tail that remain when sloughing, or the dropping off of skin occurs. Whenever a rattlesnake is agitated, it begins to move its tail, a motion that causes the rings of hardened skin to make a rattling noise. Most naturalists believe that this noise is an involuntary reaction that results from the nervousness of the reptile they do not think that the rattlesnake is attempting to convey a warning to its possible victim. Studies have revealed that the rattlesnake is the only venomous snake that gives a signal before striking and, in fact, this reptile is the only species that has rattles. However, both the bull snake and the fox snake also vibrate their tails rapidly whenever they become nervous. Whether or not the rattlesnake should be called “the gentleman among snakes” because of the noise it makes before striking is an interesting question. Which of the following statements about the rattlesnake is untrue?