How is a bridge built? Cement is mixed with water and rocks to make concrete. The concrete is poured into holes and into blocks that are stacked to make a bridge. Once fences and lights are added to the bridge, cars can drive across it.
语言 英语 ● 格式 PDF ● ISBN 9781575058115 ● 出版者 Lerner Publishing Group ● 发布时间 2004 ● 下载 3 时 ● 货币 EUR ● ID 4770717 ● 复制保护 Adobe DRM
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