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    A taxi company in one of Japan's big cities is introducing silent taxi drivers．Miyako Taxi，which is based in Kyoto，showed the new idea in March．The business is recently operating five "Silent Taxis" across the city．

    The cars look like any ordinary taxi，but a notice written on the back of the passenger seat tells passengers that they have entered one of the new silent cars．Drivers will offer a greeting when their passenger enters the car，and after making sure the route(路线)they will not start small talks．The drivers are only allowed to take their part in a conversation，only if they are spoken to first．Of course，they are also allowed to communicate in emergency(紧急的) situations．

    While introducing the idea to the public，a spokesman from Miyako Taxi said，"This service is currently in a trial(试验)period．It is introduced in order to create an in-car environment that provides the most comfortable ride for our passengers through reducing the driver's speaking．"

    According to reporters from Japan Today，an online newspaper based in Tokyo，the taxi company made the decision after hearing reports from passengers that they felt bored to be forced to chat with their drivers．

    At the end of the trial period，the company will see how popular the silent taxis are with passengers before deciding whether to roll it out across more of their drivers or not．

    党的十九大提出实施振兴乡村战略，第一次将乡村振兴提升为执政党的战略，为中国未来农村发展指明了方向。

    改革开放39年来，我国农村经济取得了巨大成就,但也存在一些问题，如农村人口占全国总人口45%，而农业增加值只占GDP的8%；2017年我国农村贫困人口依然有4000多万，城乡居民人均收入倍差是2.57；农业基本建设投资占国民经济基建投资的比重偏低等问题依然突出。

    七一村，这个与党的生日同名的乡村，20年前还是一个贫困村，如今已嬗变为浙江省乃至全国农村奔小康样本村。这一切，均得益于该村持续不断地探索乡村振兴的发展新模式。针对七一村70%村民在外经商的情况，村里统一进行了土地流转，实现农田规模经营。兴建了占地460亩集科研生产、生态休闲、游览观光于一体的七一村农业生态园。2016年年底以来，七一村开展了环境综合行动，启动了综合市场改造提升工程、部分供排水管道改造提升工程……，村民年人均收入从1997年的3700元增加到2016年的4.8万元。2017年七一村入选中国名村影响力及发展指数300佳。

上述材料反映出我国城乡经济发展中主要存在着什么问题？借鉴七一村的成功经验，就如何实施振兴乡村战略提出你的建议。

如图所示．a、b、c 是地球大气层外圆形轨道上运动的三颗卫星，a 和 b 质量相等且小于 c 的质量，则（   ）