棉纤维经丝光整理后发生了哪些变化？试解释之。

患者，女，20岁，外伤骨折后，在口内行即刻根充术后转修复科，口腔检查，冠2／3折断，不松动，根管内有充填物，叩（++）。余牙及咬合关系正常。

桩冠修复的时机，应在完善的根管治疗后至少多长时间才能进行（）。

A.即刻

B.3天后

C.1周后

D.两周后

E.1个月后

（）的存在会使烟气的露点显著升高，从而极易引起管道和空气净化设施的（）。

瑞典当地时间2017年10月3日，诺贝尔物理学奖评委会委员、瑞典皇家科学院秘书长约兰•汉森宣布，将2017年诺贝尔物理学奖授予3位美国物理学家雷纳•韦斯（RAinerWeiss）、巴里•巴里什（BArryBArish）、基普•索恩（KipStephenThorne），以表彰他们对引力波探测器LIGO的决定性贡献及其对（）的观察。2017年诺贝尔奖化学奖，颁给了雅克•杜波什（JACquesDuBoChet），约阿基姆•弗兰克（JoAChimFrAnk）和理查德•亨德森（RiChArDHenDerson），以表彰他们发展了冷冻电子显微镜技术，从而能够以接近原子分辨率水平来确定溶液里的分子结构.

A.相对波构

B.引力波

C.相引力

D.相力波

Questions 6～10

It is Monday morning, and you are having trouble waking your teenagers. You are not alone. Indeed, each morning, few of the country’s 17 million high school students are awake enough to get much out of their first class, particularly if it starts before 8 am. Sure, many of them stayed up too late the night before, but not because they wanted to.
Research shows that teenagers’ body clocks are set to as schedule that is different from that of younger children or adults. This prevents adolescents from dropping off until around 11 pm, when they produce the sleep-inducing hormone melatonin, and waking up much before 8 am when their bodies stop producing melatonin.
The result is that the first class of the morning is often a waste, with as many as 28 percent of students falling asleep; according to a National Sleep foundation poll. Some are so sleepy they do not even show up, contributing to failure and dropout rates.
Here is an idea: stop focusing on testing and instead support changing the hours of the school day, starting it later for teenagers and ending it later for all children. Indeed, no one does well when they are sleep-deprived, but insufficient sleep among children has been linked to obesity and to learning issues like attention deficit/hyperactivity disorder. You would think this would spur educators to take action, and a few have.
In 2002, high schools in Jessamine County in Kentucky pushed back the first bell to 8:40 am, from 7:30 am. Attendance immediately went up, as did scores on standardized tests, which have continued to rise each year. In Minneapolis and Edina, Minnesota, which instituted high school start times of 8:40 am and 8:30 am respectively in 1997, students’ grades rose slightly and lateness, behavioral problems and dropout rates decreases. Later is also safer. When high schools in Fayette County in Kentucky delayed their start times to 8:30 am, the number of teenagers involved in car crashes dropped, even as they rose in the state.
So why has not every school board moved back that first bell Well, it seems that improving teenagers’ performance takes a back seat to more pressing concerns: the cost of additional bus service, the difficulty of adjusting after school activity schedules and the inconvenience to teachers and parents.
But few of these problems actually come to pass, according to the Center for Applied Research and Educational Improvement at the University of Minnesota. In Kentucky and Minnesota, simply flipping the starting times for the elementary and high schools meant no extra cost for buses.
There are other reasons to start and end school at a later time. According to Paul Reville, a professor of education policy at Harvard and chairman of the Massachusetts Board of Education, "trying to cram everything out 21^th-century students need into a 19^th-century six-and-a-half-hour day just isn’t working". He said that children learn more at a less frantic pace, and that lengthening the school day would help "close the achievement gap between disadvantaged students and their better-off peers".

The phrase "takes a back seat to" (para. 6) could be best replaced by ______

A. is secondary to
B. is a prelude to
C. lends support to
D. provides a solution to

在低压操作中，人体及其所携带的工具与带电体的距离不应小于0.1m,在1OKV无遮拦操作中,此距离不应小于0.7m。