问题
单项选择题
当允许速度120km/h以下正线线路前后高低误差达到()时,应进行经常保养作业。
A、4mm
B、6mm
C、7mm
D、10mm
答案
参考答案:B
当允许速度120km/h以下正线线路前后高低误差达到()时,应进行经常保养作业。
A、4mm
B、6mm
C、7mm
D、10mm
参考答案:B
Listening to an Ipod, playing loud video games and going to see the movies are harmful to your hearing. ___71____ Block(堵住),walk and turn—that’s what hearing scientists want you to do when you face a loud noise. Block the noise from entering your ears. 72 And turn it down. About 15% of all school-age children live with some hearing loss. And it’s a growing problem. _ 73 Block It Out! 74 It starts at zero. Sounds that are too loud or sounds that last too long can harm the inner ear’s hair cells (细胞)。 Most people don’t know that listening to headphones at full volume(音量) is harmful. So turn down the volume and protect your ears. What’s Too Loud? 75 And 60 decibels is totally safe.
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