同区内敷设管道电缆可采用人工牵引，牵引电缆的拉力应均匀，不应猛拉紧拽，全塑电缆的牵引力应小于全塑电缆允许拉力的70%。( )
参考答案：错
While flying, a bat makes a sound which hits things and comes back to its ears.
In this way, it's able to know _____ the things are and avoid bumping into them. [ ]
A. how
B. where
C. what
D. which
订购成本是指企业从发出采购定单，到物资验收入库所发生的全部费用，主要包括（）。
A、占用资金所损失的利息和其他盈利
B、折旧费与维修费、保险费
C、物料的单位购入成本
D、采购的交易费
E、采购人员的差旅费
