Our teacher punished Tom for his being late for school last month. ______, Tom gets up early every day and is never late again.

A． Now and then

B．From then on

C．Till then

D．Just then

一个项目具有一个项目主管，一个项目主管可管理多个项目，则实体“项目主管”与实体 “项目”的联系属于【 】的联系。