A．Obama’s Hard Childhood

　　B．Obama Encourages Students to Carry on Studies

　　C．Obama’s Speech Met Criticism

　　D．Amazing Dropout Rate of the US

　　解析：选B 主旨大意题。本文主要介绍了美国总统奥巴马发表电视演讲呼吁学生们克服困难继续学业。B

　　(2017·云南昆明高三复习教学质量检测)The pinyon(食松)is one of the most important tree species in the American Weste often used to make sweets.But a new research suggests that man­made noise may threaten the future of the pinyon.

　　Jays(松鸦) are important spreaders of pinyon seeds.Each falles.Throughout the winter，when other food becomes short，the birds feast on hidden seeds.But some seeds never get recovered.Instead，they come out and form the next generation of trees.

　　The researchers conducted their study in a woodland of New Mexico.They spread 20 seeds under each of 12 pinyons­six in quiet spots and six in loud areas.Every day for three days，the team came back to each tree to see how many seeds had been eaten and to replenish(补充) some.They found quieter areas of the woodland were more likely to have jays and four times more with pinyon seedlings than loud regions.Meanwhileyons to survive from generation to generation.

　　The influence of the noise could be felt for many years to come since pinyons live for decades.Fewer seedlings in noisy areas might eventually mean fewer mature trees，because the trees are so slow­growing.Meanwhile，a lower thickness of pinyons would mean less critical(极重要的) habitat for the hundreds of species that depend on them for survival.【文章大意】　美国西部有一种叫做食松的树种。食松为数百种野生动物提供了食物和栖息地同时它Jays are important to the pinyon for the reason that ________．

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