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)”.

    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. ”

微信是时下流行的手机语音聊天软件，语音信息由一定频率的____ 传递，它在真空中的传播速度为____ m/s．

关注社会，探究实践。

学完《法律初探》后，七年级召开了“我与法律”的主题班会。

下面事小刚的班会记录，请你结合所学知识补充不完整部分。

【时政链接】2015年8月29日第十二届全国人民代表大会常务委员会第十六次会议，修订《中华人民共和国全国人民代表大会和地方各级人民代表大会选举法》（第六次修正），会议强调“一步到位实行城乡按相同人口比例选举人大代表”、实现城乡“同票同权”。

【法律解读】截至2015年11月25日，广东省立涉黑恶类犯罪案件数同比上升22.50%；破案10968起，同比上升95.72%；刑拘32139人，同比上升46.28%；逮捕19020人，同比上升46.15%．检察机关公诉涉黑恶被告人22340人；法院一审判决涉黑恶被告人19323人。

【感悟收获】班会结束了，它给我留下很多的思考与启迪。

下列现象中，最能说明植物生长素具有低浓度促进生长，高浓度抑制生长两重性的是（　　）

图为真空示波管的示意图，电子从金属丝K发出（初速度可忽略不计），在金属丝与A板间加以电压U₁，电子加速后，从A板中心孔沿中心线KO射出，然后进入两块平行金属板M、N间的偏转电场（电子进入时的速度方向与该电场方向垂直），离开偏转电场后打在荧光屏上一点．已知M、N两板间的距离为d，板长为L，电子的质量为m，电荷量为e，不计电子所受的重力及它们之间的相互作用力．