问题
单项选择题
十字轴可以（）上磨削。
A.切入式台阶轴无心磨床
B.切入式成形面无心磨床
C.切入式十字轴无心磨床
答案
参考答案：C
搜题请搜索小程序“爱下问搜题”
十字轴可以（）上磨削。
A.切入式台阶轴无心磨床
B.切入式成形面无心磨床
C.切入式十字轴无心磨床
参考答案：C
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| Are you carrying too much on your back at school? Lots of kids at the same age are as you are. Not only are students in China 1 from this problem,but kids in the United States are 2 fed up with(饱受……之苦) heavy school bags. Experts are starting to 3 that more and more young students are having back and neck problems as a result of school bags 4 too heavy for them. "It's hard for me to get up the 5 with my bag because it's so heavy," said Rick Hammond, 6 ll-year-old student in the US. Rick is among the students who have 7 backpacks(背包) with two straps(带子) to carry them, 8 a number of other students choose rolling backpacks. But even with rolling backpacks, 9 up stairs and buses with them is 10 a problem for kids. Many of them have hurt their knees,backs or necks because of heavy school bags. But how much is too 11 ? Experts say students should carry 12 more than 10 to 15 percent of their own body weight. Scott Bautch,a Wisconsin 13 docotor,said kids under4th grade should 14 within 10 percent. But it's also important that older kids don't go 15 15 percent,because their bones are still growing. Bautch explained that there are other injuries caused by backpacks. "Kids are 16 their balance and falling down with these backpacks,"he said. Parents and teachers are starting to tell the kids to only take 17 library books they will be reading that night.Some teachers are using worksheets (作业纸) or 18 workbooks for students to take home. One of the best answers is,as some 19 themselves suggested, to have no homework 20 ! | ||||
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