什么是无效教学？

A. should not be carried out during the watches
B. can only be carried out in port
C. is a kind of maintenances carried out prior to the occurrence
D. is a kind of maintenances carried out after the occurrence

A. 物质利益第一位
B. 提高顾客让渡价值
C. 为顾客省钱
D. 为顾客节省时间

A. 正确
B. 错误