Have you ever planted a few trees on Tree Planting Day? Each year, millions of people, both 41.______, plant a lot of trees. But this may not be the best way to make your home a 42._____ place. Last week we visited a park in Hebei. We were 43._____ to find most of the trees had been burned. The workers told us that the trees 44._____ soon after they were planted because they weren’t watered well enough. 45._____ workers burned them and cleaned the place for 46._____ trees to be planted this year. 47.______ a card found in one of the dead trees, a student wrote,” I hope this tree will grow up with me to 48.______ the backbone (栋梁) of our country.” The workers said that the survival (存活) of the trees was really more important than 49.______ trees were planted. Some people in Beijing now have a new idea that they can donate (捐赠) some money and let professional (专业人士) plant and 50.______ the trees.
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青一松 幼苗
共回答了11个问题采纳率:90.9% 举报
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A为n阶矩阵, 证:tr(A^k)=A的各个特征值的k次方之和
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你能帮帮他们吗