题目内容

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*.

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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

"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. 【C15】

A. discouraging
B. disclosing
C. discovering
D. disregarding

"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. 【C14】

A. releasing
B. absorbing
C. tracking
D. exposing

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