With his attention ---- on the book he was reading,he didn't

B
本题考查的是with的复合结构,即with+宾语+宾补.空上要填的成分是宾补.这时要看宾语和宾补之间是主动还是被动关系.本题用到一个词组：focus one's attention on sth,也就是说his attention 和focus之间是被动关系,所以选 focused