物业管理的专业化，指的是由物业服务企业通过( )签订的。
A．合同或协议 B．合同和契约C．合同和协议 D．合同或契约
参考答案：D
It was in the lab ______ was taken charge of by Pro. Harris ______ they did the experiment.
A．which; where
B．that; which
C．whom; that
D．which; that
在道路货物运输组织中，( )组织方式的基本原理体现为平行作业原则的利用。
A．双班运输
B．拖挂运输
C．甩挂运输
D．定时运输
