In many high schools, there are strict rules about using mobile phones. If your phone rings in class, for example, the teacher will be very angry.

    Every mobile phone has a ringtone (铃声). It tells you that someone is calling you. Now, there is a ringtone called "mosquitotone (蚊子铃声)". Using it, students can receive calls and text messages (短信) in class but the teacher will not realize what is happening. How?

    Mosquitotone has a special sound. Only children and teenagers can hear it. As we get older, we are unable to hear some sounds with high frequencies (频率). As a result, a child or teenager can hear the mosquitotone ringtone, but someone of 20 or older can't.

    But sometimes, people over 20 can hear the ringtone. One British student's phone uses mosquitotone. In class, the student's phone rang. The 22-year-old teacher looked at the student and became unhappy. "I heard that. You know the rule: no mobile phone in class."

    Not all the students are interested in mosquitotone. Jerry Jones, a high school student of 17, says, "Using mosquitotone too often is bad for our hearing. I may use it for pleasure, but not in class. It's unfair(不公平的) to the teachers!"

    What do parents think of mosquitotone? "I think it is perfect for places like movie theaters," says Connie Neeson, 44. "Think about it. You're watching a film and someone's mobile phone rings. Mosquitotone is good because many people don't hear it. However, it also has a bad influence（影响） on their study if students use it in class."

    There are millions of different animals in the world, but some are in danger, and some may soon die out. People can never see them again. Mark and David wanted to find some of these rare animals, so they climbed mountains, crossed rivers, and walked through rainforests.

    A Bat, a Cat or a Squirrel?

    Mark and David found the aye-aye. The aye-aye has bright eyes. It has ears like a bat, a body like a cat and a tail(尾巴) like a squirrel. Some people think the aye-aye brings bad luck. They killed(杀死) many of them, and cut down a lot of trees where the aye-aye lives as well.

    A Strange Parrot

    Mark and David found the biggest parrot in the world that cannot fly. Many years ago, some animals came to the place the parrots lived in, and killed many of them. Now there are only a few left.

    Another Special Animal

    Mark and David went looking for a manatee. A manatee looks like a seal and a hippo. In some places where manatees live, the water in the river gets low. Then the manatee swims to the place where there is more water. Many get stranded(搁浅), and some are killed by other animals and people, too.

    After Mark and David returned, they made a film about these animals. They want to show the world these strange but interesting animals. They want the world to know there are not many of them left, and they all have a place in our world.

    If you ask soma people, "How did you learn English so well?" You may get a surprising answer, "In my sleep!"

    These are people who have taken part in one of the recent experiments to test "Learn-While-Sleep" methods, which are now being tried in several countries, and with several subjects, of which English is only one.

    Specialists say that this "sleep study" method speeds language learning greatly. They say the average person can learn two or three times as much during sleep as in the same period (时期) during the day, and does not affect his rest in any way, A word of warning, however, that sleep teaching will only strengthen in your mind what you have studied already while you are awake.

    In an experiment. lessons were broadcast (广播) over the radio. Each lesson lasted twelve hours from 8: 00 p. m. to 8: 00 a. m. The first three hours of English grammar and vocabulary were given with the students awake. At 11: 00 p. m. a lullaby was broadcast to send the student to sleep and for the next three hours the radio whispered the lesson again into his sleeping ears. At 2: 00 a. m. a sharp noise was sent over the radio to wake the sleeping student up for a few minutes to review the lesson. The cradlesong (a kind of soft song making you fail asleep easily) sent him back to rest again while the radio went on At 5: 00 a. m. his sleep ended and he had to go through the lesson again for three hours before breakfast.