13．Because they hadn’t booked a room in advance, there were _____ left when they arrived at the hotel.

A．none

B．no one

C．Nobody

D．Nothing

出版社选题计划的具体作用不包括（）。

A.兼顾两个效益

B.优化出书结构

C.监控经营活动

D.确定出书规模