题目

化学是一门以实验为基础的学科，为保证实验的安全、顺利完成，要特别注意一些操作事项。下列是初中化学实验中常见的操作事项，其中描述不正确的是A．稀释浓硫酸，将浓硫酸沿烧杯内壁慢慢注入水中，并用玻璃棒不断搅拌B．粗盐提纯中蒸发结晶，要边用酒精灯加热边用玻璃棒搅拌，直到将水蒸干为止C．测定空气中氧气的体积，将点燃的过量红磷迅速伸入集气瓶（或广口瓶）中，并塞紧橡皮塞D．用高锰酸钾制氧气并用排水法收集气体，待气泡根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。Training for a marathon requires careful preparation and steady, gradual increases in the length of the runs. , buy the best-fitting running shoes you can find. No one can say which brand will work best for you or feel best on your feet, so you have to rely on your experience and on the feel of each pair as you shop. When you have found shoes that seem right, walk in them for a few days to double-check the fit. As always, you should stretch(伸展) at least ten minutes before each run to prevent injuries.During the first week, do not think about distance, but run five minutes longer each day. , it is wise to take a day off to rest. But during the next week, set a goal of at least a mile and a half per run. . After two weeks, start timing yourself. . Depending on the kind of race you plan to enter, you can set up a timetable for the remaining weeks before the race.A. After six daysB. For a good marathon runnerC. Before you begin your trainingD. With each day, increase the distance by a half mileE. If they still feel good, you can begin running in themF. Time spent for preparation raises the quality of trainingG. Now you are ready out a goal of improving distance and time