It's Saturday morning. My parents and I are on a tour bus. There are about twenty people on the bus. Some are from America, and some are from England and Australia. They are all our friends. We are going to the Great Wall. On the bus, there are two Chinese. One is a woman, the other is a man. The woman is good at English. She is talking with us about the Great Wall. The other people are listening to her. They like the Great Wall. They want to see it very much.

有一种新型锁﹣﹣声纹锁．只要主人说出事先设定的暗语就能把锁打开，别人即使说出暗语也打不开．这种声纹锁辨别声音的主要依据是（  ）