运输布局的主要依据有()。A.自然条件 B.国家政策 C.国民经济的发展水平 D.科

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.

8().

A. tenant

B. determinant

C. lubricant

D. repentant

苹果每千克3元，梨每千克4元，苹果和梨各买5千克，一共需要多少元它的列式是：3×4×5=60元[ ]

当导体两端电压为3V时，通过导体的电流为0.1A，该导体的电阻是____Ω。若使导体中的电流为0.5A，则导体两端的电压是______V，此时导体的电阻是______Ω。

3亿4千5百万用科学记数法表示是______．

抗血清特异性的鉴定方法（）

A.对流免疫电泳和区带电泳

B.单向琼脂扩散和免疫电泳

C.火箭电泳和血凝法

D.凝胶电泳和血凝法

E.双向琼脂扩散及免疫电泳