A:where; which
B:that; that
C:where; that
D:which; that
“其法,烧生铁精以重柔铤,数宿则成钢。以柔铁为刀脊,浴以五牲之溺,淬以五牲之脂”。材料描述的冶炼技术最早出现在( )