恩格斯说：“就世界性的解放而言，人工取火的进步超过了蒸汽机。”在我国古代最早采用人工取火的是

A．元谋人

B．北京人

C．河姆渡人

D．山顶洞人

A device used to enlarge the size of an existing bore hole，having teeth arranged on its outside circumference to cut the formation as it rotates is a（n）（）.

A.Enlarger bit

B.Casing bit

C.Hole opener

D.Casing opener