题目

．实验室制取氧气不正确的操作是（ ） A．装药品前检查装置的气密性 B．导管口开始有气泡冒出时，不宜立即收集气体 C．停止加热时，应先把导管移出水面，然后熄灭酒精灯 D．收集满氧气的集气瓶从水槽中取出后倒放在桌面上 答案：【考点】制取氧气的操作步骤和注意点． 【分析】正确的实验操作是实验成功的保证．解这类问题我们不仅要掌握正确的操作方法，而且还应了解这样操作的原因以及错误操作可能造成的后果． 【解答】解：实验室制取气体，都应先检查装置的气密性，确定装置不漏气，才能加药品； 用排水法收集时  In the early days of the American West,life was difficult. People lived on farms far a 1       from other families. They went to town once a week o 2       once a month. Then they saw their friends and n 3      . On the farms everyone had lots of work to do.  And there was a big problem. One family couldn't build a house a 4           Then,what did families do to build houses? They asked their friends and neighbors for h 5       They i 6       them to work in a group for a few days. The women cooked t 7       The men work on the buildings. For the children,it was like a holiday. There were many other c 8       to play with. Together these people built a house. They enjoyed w 9       together. At another time the family with the new house would help their neighbors.  Why don't we work with others? It can be fun and life can become e 10       ,too.1.a       2. o       3. n       4. a       5. h         6.i       7. t       8. c      9. w       10. e