The writer was _____ in his writing that he forgot to flick the ashes from his cigar.

　　 A concentrated　　 B devoted　　 C absorbed　　D fixed

中国古代有个统一王朝，它最先在全国范围内推行了郡县制，建立起中央集权制的政治模式。据此判断，这个王朝是( )。

A．西周
B．秦朝
C．东汉
D．明朝