现需要物质的量浓度约为2 mol·L－1的NaOH溶液100 mL，下面的操作正确的是( )
A．称取7.8 g Na2O2固体，放入250 mL烧杯中，用100 mL 量筒量取100 mL蒸馏水，加入烧杯中，同时不断搅拌至固体溶解
B．称取8 g NaOH固体，放入100 mL量筒中，边搅拌边慢慢加入蒸馏水，待固体完全溶解后用蒸馏水稀释至100 mL
C．称取8 g NaOH固体，放入100 mL容量瓶中，加入适量蒸馏水，振荡容量瓶使固体溶解，再加入水到刻度，盖好瓶塞，反复摇匀
D．用100 mL量筒量取40 mL 5 mol·L－1NaOH溶液，倒入250 mL烧杯中，再用另一量筒量取60 mL蒸馏水，不断搅拌下，慢慢倒入烧杯中
答案：D
A不正确，因为过氧化钠要消耗水；B不正确，量筒不能稀释溶液；同样容量瓶也不能稀释溶液，C不正确，因此正确的答案选D。
| 完形填空：从A、B、C中选择一个最佳答案，使短文意思完整。 | |||
| Mr Chen is a farmer who 1 in western China with his wife and two sons. One year ago, he discovered that he had cancer. The doctor told him that he needed an operation at once. And he said the operation would 2 thousands of yuan. It was too much money for Mr Chen and his wife. They had no job and 3 their sons were at school. The situation seemed 4 . Two weeks later, however, Mr Chen got some good news. He was told about a health care project which provides medical treatment 5 poor patients in western China. They need to pay only half the cost or even less. Thanks to the project and the kindness of his family and neighbours, he was able to receive an operation just 6 to prevent the illness from getting worse. Now he has returned to his family. The 7 of this health care project is to improve the situation for poor people in western China. So far, the project has helped more than 5,000 people 8 medical aid. The Chinese government is 9 working together with other countries and international organizations to do this. They hope to develop a new health care model 10 China. As our country develops, we must remember the responsibilities (责任) of caring for the weakest members. | |||
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