90.美国宪法要求总统是生于美国本土的公民，三十五岁以上，并且在美国居住了至少十四年。

90. The United States Constitution requires that President be a natural-born citizen, thirty-five years of age or older, who has lived in the United States for a minimum of fourteen years.

89.由于空间不足，艺术博物馆在考虑购买和接受捐赠的艺术品是越来越慎重，有些情况下放弃其进一步改善收藏的机会。

89. Because of the space crunch, the Art Museum has become increasingly cautious in considering acquisitions and donations of art, in some cases passing up opportunities to strengthen is collections.

88.当有关西部铁路的说服和规划工作终于完成后，真正艰难的任务还没有开始；即危险，吃力，需要伤筋动骨和吵吵嚷嚷的建造这些铁路的实际工作。

88. When the persuading and the planning for the western railroads had finally been completed, the really challenging task remained: the dangerous, sweaty, backbreaking, brawling business of actually building the lines.

87.在伊利诺州Angonne市的一个废弃煤矿的三年研究取得了成果，科学家们相信这些成果可以帮助改造把美国产煤区弄得伤痕累累的数千个旧煤场。

87. Three years of research at an abandoned coal mine in Argonne, Illinois, have resulted in findings that scientists believe can help reclaim thousands of mine disposal sites that scar the coal-rich regions of the United States.

86.人造花卉即可用于科学目的，也可用于装饰目的，它们可以用各种各样的材料制成，臂如蜡和玻璃；其制作如此精巧，几乎可以以假乱真。

86. Artificial flowers are used for scientific as well as for decorative purposes. They are made from a variety of materials, such as way and glass, so skillfully that they can scarcely be distinguished from natural flowers.