发现起重机故障时，需先切断总电源。

The effect of the baby boom on the schools helped to make possible a shift in thinking about the role of public education in the 1920’s. In the 1920’s, but especially (1) the Depression of the 1930’s, the United States experienced a (2) birth rate. Then with the prosperity (3) on by the Second World War and the economic boom that followed it, young people married and (4) households earlier and began to (5) larger families than had their (6) during the Depression. Birth rates rose to 102 per thousand in 1946, 106.2 in 1950, and 118 in 1955. (7) economics was probably the most important (8) , it is not the only explanation for the baby boom. The increased value placed (9) the idea of the family also helps to (10) this rise in birth rates. The baby boomers began streaming (11) the first grade by the mid-1940’s and became a (12) by 1950. The public school system suddenly found itself (13) The wartime economy meant that few new schools were buih between 1940 and 1945. (14) , large numbers of teachers left their profession during that period for better-paying jobs elsewhere.

(15) , in the 1950’s, the baby boom hit an antiquated and inadequate school system. Consequently, the custodial rhetoric of the 1930’s no longer made (16) ; keeping youths ages sixteen and older out of the labor market by keeping them in school could no longer be a high (17) for an institution unable to find space and staff to teach younger children. With the baby boom, the focus of educators (18) turned toward the lower grades and back to basic academic skills and (19) . The system no longer had much (20) in offering nontraditional, new, and extra services to older youths.

3().

A. took

B. produced

C. brought

D. carried

读“美国略图”，回答下列问题．

（1）美国西部有一系列南北走向的山脉，它们都是_______山系的一部分．

（2）根据流向，可判断密西西比河的地势北部要比南部______．

（3）五大淡水湖中，全部位于美国境内的是______湖，其余是美国与______（国家）共有的．

（4）五大淡水湖就其成因而言，是地质史上由______作用形成的．

（5）A处是美国西部的大港口，其名称是______，附近的“______”是新兴的电子工业中心．“9、11”恐怖组织袭击撞毁的世贸大楼所在的城市是______．

（6）美国东北部因有丰富的______、______等矿产资源，以及_______洋沿岸的优良港口和______河便利的水运条件，而成为美国最早开发的工业区．

（7）美国的本土部分主要位于五带中的______带，气候以______气候为主．

（8）美国的交通中心是______，汽车工业中心是______．

（）主要用由金属制成的各种形状的支架展示样品和陈列商品。

A、支架陈列

B、平放陈列

C、地面、地台陈列

D、柜架陈列

细胞型胚乳

根据《中华人民共和国教育法》的规定，我国学校的（）必须由具有我国国籍、在我国境内定居、并具有国家规定任职条件的公民担任。

A.教师

B.校长

C.行政人员

D.管理人员