please help有条语法题我不明白请帮忙

kevinhu

until the eighteenth century,charcoal was --------used in blast furnaces,as well as in glassmaking,blacksmithing,and metalworking.

A)what the chief fuel

B)the chief fuel that

C)the chief fuel was

D)the chief fuel

为什么选D不选B，我好疑惑啊，请帮帮小弟

gre3333

the chief fuel (that was)

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酷小牛

agree

dengfu

until the eighteenth century,charcoal was --------used in blast furnaces,as well as in glassmaking,blacksmithing,and metalworking.

A)what the chief fuel

B)the chief fuel that

C)the chief fuel was

D)the chief fuel

选D，后面的used...过去分词做后直定语，修饰chief fuel； 选B是当成定语从句，但是差了一个be动词was