用户在电价低的供电线路上擅自接用电价高的用电设备，应承担怎样的违约责任？

As one of the tools and techniques of activity sequencing, a lead ______ .

A．directs a delay in the successor activity

B．could be accomplished by a finish to-start relationship with a delay time

C．means the successor activity cannot start until after the predecessor is completed

D．allows an acceleration of the successor activity