题目

如图为实验室培养和纯化大肠杆菌过程中的部分操作步骤,下列说法错误的是( ) A.①步骤使用的培养基已经灭菌并调节过pH B.①②③步骤操作时需要在酒精灯火焰旁进行 C.④在恒温培养箱中培养时需要将平板倒置 D.④操作过程中,需灼烧接种环5次 答案：D 解析：由题图可知,①是倒平板,②是用接种环蘸取菌液,③是进行平板划线,④是培养结果。①步骤表示倒平板,在倒平板之前培养基已经灭菌并调节过pH,A项正确;①②③步骤操作时需要在酒精灯火焰旁进行,防止被杂菌污染,B项正确;将④放在恒温培养箱中培养时,需要将平板倒置,防止皿盖上的冷凝水滴落污    Great changes have been made in family life because of science and industry.     In the past, when more Americans live on farms, the typical family had many children. In a farm family, parents and their children often lived with grandparents. Often, too, uncles and aunts lived nearby. But when industry became more important than agriculture in American life, families became smaller because industry requires workers who are ready and able to move off the land and to move again whenever necessary. And large families cannot be moved from place to place as smaller families can. So, at present people tend to have smaller families.     In the future, because of industrialization, a typical family will be required to move even more often than now. So families will be even smaller. The typical family may remain childless and consist only of a man and a woman. A small number of families may take raising children as their chief work. At the same time they may also raise other people’s children, leaving families free to move from job to job. 1．The main topic discussed in the passage is________ A．the development of science and industry in America B．the influence of science and industry on American families C．the harmful effect of industrialization D．the social problems resulting from the highly developed science and industry in .America 2．________ are described in the passage. A．Families of the past B．Families of the present and of the future C．Families of the past and of the future D．Families of the past, the present and the future 3．According to the writer, one of the reasons that families are getting smaller in America is that________ A．children tend to leave their parents and grandparents when they grow up B．people stop caring for having children C．the need for workers who are able to move at any time has been increasing D．both old and young people like to live by themselves 4．________ will be in charge of raising children in the future. A．Most families B．All families C．Social workers D．A small number of families 5．From  the  passage,  we  can  conclude  that________ A．science and industry have caused thousands of families to separate B．children do not like to live with their parents or grandparents C．large families can hardly exist in modern society D．Americans are very careful in choosing their jobs