填空题 During the 19th century, natural gas was used on a local scale because of the difficult situation in
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【正确答案】 1、transportation，

【答案解析】[解析] 本题涉及19世纪时天然气资源只能在当地使用的原因。小标题From Field to Ford下第二段首句Throughout the 19th century，the use of natural gas remained localized because there was no way to transport large quantities of gas over long distances transport large quantities of gas over long distances为答案出处。