In the United States, the first day nursery, was opened in 1854. Nurseries were established in various areas during the 1 half of the 19th century; most of 2 were charitable. Both in Europe and in the U.S., the day nursery movement received great 3 during the First World War, when 4 of manpower caused the industrial employment of unprecedented (前所未有) numbers of women. In some European countries nurseries were established 5 in munitions (军火) plants, under direct government sponsorship. 6 the number of nurseries in the U.S. also rose 7 , this rise was accomplished without government aid of any kind. During the years following the First World War, 8 , federal, State, and local governments gradually began to exercise a measure of control 9 the day nurseries, chiefly by 10 them.The 11 of the Second World War was quickly followed by an increase in the number of day nurseries in almost all countries, as women were 12 called up on to replace men in the factories. On this 13 the U.S. government immediately came to the support of the nursery schools, 14 $6,000,000 in July, 1942, for a nursery school program for the children of working mothers. Many States and local communities 15 this Federal aid. By the end of the war, in August, 1945, more than 100, 000 children were being cared 16 in daycare centers receiving Federal 17 . Soon afterward, the Federal government 18 cut down its expenditures for this purpose and later 19 them, causing a sharp drop in the number of nursery schools in operation. However, the expectation that most employed mothers would leave their 20 at the end of the war was only partly fulfilled.
A. sources
B. abundance
C. shortage
D. reduction
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设A是3阶实对称矩阵,特征值是0,1,2.如果λ=0与λ=1的特征向量分别是α1=(1,2,1)T与α2=(1,一1,1)T,则λ=2的特征向量是__________.
设α0是A属于特征值λ0的特征向量,则α0不一定是其特征向量的矩阵是
A. (A+E)2.
B. 一2A.
C. AT.
D. A*.
设A是3阶不可逆矩阵,α1,α2是Ax=0的基础解系,α3是属于特征值λ=1的特征向量,下列不是A的特征向量的是
A. α1+3α2.
B. α1一α2.
C. α1+α3.
D. 2α3.
"Forests are the lungs of our land," said Franklin Delano Roosevelt. Twenty years ago, the world"s lungs were diseased. Roughly half of all the planet"s once-luxuriant tropical forests had been felled and the further deterioration of the Earth"s green spaces seemed【C1】______. Over time countries【C2】______ a "forest transition curve". They start in【C3】______with the land covered in trees. As they get richer, they fell the forest and the curve drops sharply until it reaches a low point when people decide to【C4】______whatever they have left Then the curve rises as reforestation【C5】______. At almost every point along the【C6】______, countries are now doing better deforested are【C7】______down less; reforesters are【C8】______more. This matters to everyone because of the extraordinary【C9】______that tropical forests make to reducing carbon emissions. Trees are carbon【C10】______. If you fell and burn them, you【C11】______ carbon into the atmosphere. If you let them【C12】______they store carbon away in their trunks for centuries. Despite decades of【C13】______, tropical forests are still【C14】______about a fifth of emissions from fossil fuels each year. Encouraging countries to plant trees (or【C15】______ them from logging) is by far the most【C16】______way of reducing greenhouse-gas emissions.【C17】______Brazil had kept on felling trees as rapidly as it was cutting them【C18】______in 2005, it would, by 2013, have put an extra 3.2 billion tonnes of carbon dioxide into the atmosphere. As a way of【C19】______the environment, protecting trees is hard to beat. It is in everyone"s interest to find out which forest policies work—and【C20】______them. 【C18】
A. in
B. down
C. across
D. through