单选题 From the 440 radio channels available on Osaka Yusen Broadcasting, Japan's largest cable- radio network, subscribers (订户) can tune into a channel featuring (以……为特色) 24 hours of croaking frogs, or one that consists of the sound of trains polling in and out of stations.
As well as the sounds of birds or percolating (过滤) coffee, Osaka Yusen offers nearly 100 channels of announcer-free jazz, rock, classical music, Second World War military marches, and folk music from all over the world. Easton and Abba each have entire channels to themselves, al- though the repeating rate must be almost as high as that of an in-flight music channel.
For those in search of more intellectual (智力的) background sounds for their dinner par- ties, there is always the lesson channel or a range of talks on spiritual development. But anyone tired of all the above should adjust their sets to "drowsing (瞌睡) channels" and tune into the sheep-counting station, for example, which features a mature male voice slowly counting from one to a thousand.
For busy people wishing to calm down after an awful day at work, there is a channel of slow music, and another carrying only the sound of a mother's heartbeat. According to the company, "Babies listen to this noise before they are born. It's a natural relaxant./

单选题 Among the 440 radio channels available on Osaka Yusen Broadcasting, 100 channels ______.

单选题 If you are suffering from insomnia (失眠), you may tune into a channel feature ______.

单选题 Why busy people prefer a channel carrying only the sound of a mother's heartbeat?

单选题 We can learn from the passage that ______.

单选题 The passage is written for all the purposes EXCEPT ______.